Monthly Archives: September 2022

Conservation of Plants and Animals Class 8 Science NCERT Textbook Questions

Question 1.
Fill in the blanks.
(a) A place where animals are protected in their natural habitat is called ______
(b) Species found only in a particular area is known as ______
(c) Migratory birds fly to faraway places because of ________ changes.
Answer:
(a) Wildlife sanctuary
(b) endemic species
(c) climatic

Question 2.
Differentiate between the following.
(a) Wildlife sanctuary and biosphere reserve

Wildlife sanctuary	Biosphere reserve
The area reserved in a forest for the protec­tion of wild animals.	The area meant for the protection or conservation of the biodiversity. It also helps in maintaining the culture of that area.

(b) Zoo and wildlife sanctuary

Zoo	Wildlife sanctuary
A place where animals are protected in an artificial habitat, for an exhibition.	A protected area where animals live in their natural habitat.

(c) Endangered and Extinct species

Endangered species	Extinct species
The species of animals whose numbers are diminishing to such a level that they might face extinction.	The species of animals whose number is zero because of changes in their habitat and other calamities.

(d) Flora and Fauna

Flora	Fauna
The plants which are found in a particular area; e.g.Jamun, sal, etc.	The animals which are found in a particular area; e.g., leopard, cheetah, elephant, etc.

Question 3.
Discuss the effects of deforestation on the following:
(a) Wild animals
(b) Environment
(c) Villages (Rural areas)
(d) Cities (Urban areas)
(e) Earth
(f) The next generation
Answer:
(a) Wild animals: Trees are the habitats as well as sources of food for the wild animals. Deforestation leads to the destruction of the natural habitats of wild animals.

(b) Environment: Deforestation increases the temperature and pollution level of the environment. With the increase in the carbon dioxide level and a decrease in the oxygen level, it gives rise to global warming. It also lowers the level of ground water. Moreover, deforestation decreases the soil fertility and so, increases the chances of natural calamities.

(c) Villages (Rural areas): The decline in rainfall, the decrease in soil fertility, and the chances of natural disaster affect the village life.

(d) Cities (Urban areas): Deforestation result in global warming. It also results in the increase in the level of pollution. Hence, deforestation affects the life in cities.

(e) Earth: Deforestation decreases the fertility of soil. It changes the physical properties of soil. All these changes result in desertification.

(f) The next generation: Deforestation will majorly affect the life of next generation. The next generation will face problems at every step. Climatic conditions will be adversely affected. There will be scarcity of food and clean environment. Next generation won’t be able to see most of the animal species due to habitat loss.

Question 4.
What will happen if

1. we go on cutting trees
2. the habitat of an animal is disturbed.
3. the top layer of soil is exposed.

Answer:

1. If we go on cutting trees, then:
   • the temperature will increase to a greater extent.
   • the chances of natural disaster to occur will increase.
   • the water cycle will get disturbed.
2. If the habitat of an animal is disturbed, then:
   • the animals will lose their natural habitat and will reach the level of being endangered.
   • most of the animals may be forced to invade places meant for human living in search of food and shelter.
3. If the top layer of soil is exposed, then:
   • the exposed layer will lose all its nutrients, especially the hummus.
   • the water holding capacity of soil will decrease.
   • desertification will take place.

Question 5.
Answer in brief.

1. Why should we conserve biodiversity?
2. Protected forests are also not completely safe for wild animals. Why?
3. Some tribals depend on the jungle. How?
4. What are the causes and consequences of deforestation?
5. What is Red Data Book?
6. What do you understand by the term migration?

Answer:

1. The variety in life existing on the earth, their inter-relationships, and their relationships with the environment is referred to as biodiversity. We should conserve biodiversity so as to maintain the food chain. The disturbance in the food chain may affect the whole ecosystem.
2. Since capturing and killing of animals by poachers is still rampant in protected forests and areas, so they are not safe for wild animals.
3. Some tribes depend on the jungle for the fulfillment of their basic needs of life, such as food, medicine, clothing, shelter, etc.
4. The causes of deforestation may be the following:
   • Natural causes like forest fires, droughts, etc.
   • Building factories and houses.
   • Procuring land for cultivation.
   • Making furniture and using wood as fuel.
     The consequences of deforestation are:
   • Natural calamities like floods, etc.
   • Increase in the temperature of the earth, i.e., global warming.
   • Change in the physical properties of soil.
   • A decrease in groundwater level.
   • Extinction of many flora and fauna.
5. Red Data Book is a sourcebook which keeps records of all endangered plants and animals.
6. Migration means the movement of a species from its own habitat to some other place during a certain period in a year for breeding or to overcome some climatic conditions.

Question 6.
In order to meet the ever-increasing demand in factories and for shelter, trees are being continually cut. Is it justified to cut trees for such projects? Discuss and prepare a brief report.
Answer:
It’s not justified to cut trees just to fulfill our needs. Trees are known as ‘the lung of the earth’. They are the habitat of many living organisms, including animals. They give us oxygen, and maintain the O₂-CO₂ balance as well. They firmly bind the soil and hence prevent soil erosion. They also reduce the chances of natural disasters like floods and droughts. They help conserve our rich biodiversity. The cutting of trees causes an increase in the carbon dioxide (CO₂) level, which results in global warming. Moreover, it causes soil erosion, floods, the greenhouse effect, etc. Hence, trees must be protected.

Question 7.
How can you contribute to the maintenance of green wealth of your locality? Make a list of actions to be taken by you.
Answer:
By taking up the following actions, I can contribute to the maintenance of green wealth of my locality by:

• Planting saplings and trees.
• Not throwing the garbage on the streets.
• Forbidding others to cut trees.
• Making people aware of the significance of a clean and green environment.
• Watering the plants regularly and taking proper care of them.
• Reusing and recycling paper to save trees, energy, and water.

Question 8.
Explain how deforestation leads to reduced rainfall.
Answer:
Trees give out a huge amount of water in the form of water vapour during transpiration. The reduction of water vapour affects cloud formation and thus, results in less rainfall.

Question 9.
Find out about national parks in your state. Identify and show their location on the outline map of India.
Answer:
Consider the map given below:

Question 10.
Why should paper be saved? Prepare a list of ways by which you can save paper.
Answer:
A large number of trees can be saved by saving paper. This will also save water that is used to manufacture paper. Moreover, the harmful chemicals used in papermaking will show their least effects on human beings and other organisms.
Some ways to save paper are the following:

• recycling of paper.
• economical use of paper.
• paper should not be burnt.

Question 11.
Complete the word puzzle.
Down
1. Species on the verge of extinction.
2. A book carrying information about endangered species.
5. Consequence of deforestation.
Across
1. Species which have vanished.
3. Species found only in a particular habitat.
4. Variety of plants, animals and microorganisms found in an area.
Solution:

Conservation of Plants and Animals Class 8 Science NCERT Intext Activities Solved

Activity 1

Add more causes of deforestation to your list and classify them into natural and man-made.
Solution:
Natural causes of deforestation:
(i) Forest fires
(ii) Severe drought
Man-made causes of deforestation:
(i) Wood for the manufacturing of paper.
(ii) Wood for fuel and the making of houses.

Activity 2
Animal life is also affected by deforestation. How? List the points and discuss them in your class.
Solution:
(i) Due to deforestation, a great disturbance is caused in the food chain.
(ii) Deforestation makes the animals homeless.
(iii) Due to deforestation, animals become easy prey for hunters.
(iv) Herbivorous animals face the scarcity of food due to deforestation.
(v) Animals face bad effects of natural calamities.

Activity 3

Find out the number of national parks, wildlife sanctuaries and biosphere reserves in your district, state and country. Record in Table 7.1. Show these areas in an outline map of your state and India.
Protected Areas for Conservation

Protected Areas	National Park	Wildlife Sanctuary	Biosphere Reserve
In my district
In my state
In my country

Solution:
Do it yourself.

Activity 4

List the factors disturbing the biodiversity of your area. Some of these factors and human activities may disturb the biodiversity unknowingly. List these human activities. How can these be checked? Discuss in your class and write a brief report in your notebook.
Solution:
Cutting of trees, rising air, water and land pollution, excessive construction, using more resources or their products affect the biodiversity harshly.

Activity 5

Try to identify the flora and fauna of your area and list them.
Solution:
Flora (trees and plants): Pipal, sal, teak, kadamb, babool, mango, guava, ferns, arjun, keekar, etc., are flora present in our locality.
Fauna (animals): Blue-bull, chinkara, cheetal, deer, leopard, wolf, wild dog, etc., are the fauna present in our locality.

Activity 6

Find out the endemic plants and animals of the region where you live.
Endemic plants: Mahua, wild mango, sal, jamun, etc.
Endemic animals: Bison, Indian giant squirrel, etc.

Activity 7
Visit a nearby zoo. Observe the conditions provided to the animals. Were they suitable for animals? Can animals live in an artificial setting instead of their natural habitat? In your opinion, will the animals be comfortable in a zoo or in their natural habitat?
Solution:
A zoo tends to provide suitable conditions for the animals to live in, similar to their natural habitat.
Yes, animals can live in an artificial setting instead of their natural habitat, as they live in natural environment and stay protected*from people.
As per my opinion, animals are safer in the zoo in comparison with their natural environment, because special care is taken for the animals in the zoo. But I think animals feel more comfortable to live in their natural habitat as no one wants to live in prison.

NCERT Solutions for Class 8 Science Chapter 7 – 1 Mark Questions and Answers

Question 1.
What is meant by deforestation ?
Answer:
Deforestation means clearing of forests,and using that land for other purpose like building houses and factories.

Question 2.
What is meant by biosphere ?
Answer:
Biosphere is that part of the earth in which living organisms exist or which supports life.

Question 3.
Define biodiversity.
Answer:
Biodiversity means the variety and variability of all microorganisms, plant and animal life.

Question 4.
Name two animals which have become extinct. [NCT 2011]
Answer:
The mountain quail of Western Himalyas and the pink head duck.

Question 5.
What are Biosphere reserves ?
Answer:
Biosphere reserves are the areas meant for conservation of microorganisms, plants and animals.

Question 6.
Define species.
Answer:
Species is a group of individuals which are capable of interbreeding with each other.

Question 7.
What are endemic species ?
Answer:
Endemic species are exclusively found in a particular area only in small numbers.

Question 8.
What is meant by Wildlife sanctuaries ?
Answer:
Wildlife sanctuaries are some areas where wild animals are protected and preserved

Question 9.
What are National Parks ?
Answer:
National parks are reserves that protect the flora and fauna of the place.

Question 10.
Why has the survival of some animals become difficult ?
Answer:
Survival of some animals has become difficult because of changes in their natural habitat.

Question 11.
What is meant by ecosystem ?
Answer:
An ecosystem comprises of all the plants, animals and microorganisms in an area along with non-living components such as climate, soil, river, etc.

Question 12.
What is Red Data Book ?
Answer:
Red Data Book is the source book which keeps a record on population status of the species included in the Red List.

Question 13.
What are migratory birds ?
Answer:
Birds who cover long distances to reach another land are known as migratory birds.

Question 14.
Name the first Reserve Forest of India.
Answer:
Satpura National Park.

Question 15.
Name two wildlife sanctuaries of India.
Answer:
Kangha and Sultanpur.

Question 16.
Kaziranga and Corbett are …………. of India.
Answer:
National parks.

Question 17.
Name two endangered species of animals.
Answer:
The bison and antelope are endangered species of animals.

Question 18.
Why should soil be conserved ?
Answer:
Soil should be conserved to maintain the fertility of the soil.

Question 19.
Name two animal species which have become extinct in the past years.
Answer:
Dodo and thylacine.

Question 20.
Give one word for species found only in a particular area.
Answer:
Endemic species.

NCERT Solutions for Class 8 Science Chapter 7 – 2 Mark Questions and Answers

Question 1.
Why do we feel the need for conserving natural resources more than our ancestors did ? Give two reasons.
Answer:
We have to conserves the natural resources because :

• the population of the world has increased.
• as man has progressed his needs have increased.

Question 2.
Differentiate between the following : [NCERT]

1. Wildlife sanctuary and Biosphere reserve.
2. Zoo and Wildlife sanctuary.
3. Endangered and Extinct species.
4. Flora and Fauna.

Answer:

1. Wildlife sanctuary is a reserve area where wild animals are protected and preserved.
   Biosphere reserves are the areas meant for conservation of biodiversity, i.e., variety of plants, animals and microorganisms. .
2.  Zoo is a place where animals live in artificial settings for public display. Wildlife sanctuary is a place where animals live in their natural habitat within a protected area.
3. Endangered species are those whose number are diminishing and are facing extinction. Extinct species are those which are already finished.
4. Flora are the plants found in a particular area and fauna are the animals found in a particular area.

Question 3.
What is the role of small animals in the ecosystem ?
Answer:
The role of small animals is important because they form a part of the food chain and food webs.

Question 4.
Name the flora and fauna of Pachmarhi Biosphere Reserve.
Answer:
Flora – Sal, teak, mango, jamun, silver fern, arjun.
Fauna – Chinkara, blue bull, barking deer, cheetah, leopard, wild dog, wolf.

Question 5.
Name two endemic flora and endemic fauna of Pachmarhi Biosphere Reserve.
Answer:
Endemic flora – Sal and wild mango
Endemic fauna – Bison, Indian giant squirrels and flying squirrels.

Question 6.
Give two reasons why sanctuaries should be maintained.
Answer:

• Sanctuaries are places where killing (poaching) or capturing of any animal is strictly prohibited.
• Sanctuaries provide protection and suitable living conditions to wild animals.

Question 7.
What are Rock shelters ? Where are they found ?
Answer:
Rock shelters are found inside the Satpura National Park. These are the prehistoric evidences of human life in these jungles, which give us an idea about the life of primitive humans.

Question 8.
What is Project Tiger ? What is its objective ?
Answer:
Project Tiger was launched on 1st April 1973 by our government to protect the tigers of the country.

Question 9.
Why should paper be saved ?
Answer:
We should save paper because it takes 17 full grown trees to make one tonne of paper.

Question 10.
How can we save paper ?
Answer:
We should reuse used paper and recycle it.

Question 11.
How can the resources be conserved ?
Answer:
Resources can be conserved by :

• not wasting the resources.
• maintaining their quality

Question 12.
Which factors are responsible for cutting of forest ?
Answer:
As man’s need for land used in housing and farming and wood for fuel and construction increased, he started cutting down forests.

Question 13.
Expand

• WWF
• IUCN

Answer:

• World Wildlife Fund.
• International Union for Conservation of Nature and Natural Resources

Question 14.
How can overgrazing destroy forests ?
Answer:
Due to overgrazing, the young trees get eaten or killed by trampling. The lower leaves are eaten up and the roots and trunks are injured by cattle.

Question 15.
How does vegetation help to conserve water ?
Answer:
Vegetation slows down the flow of rain water on land and increases the absorption of water by the soil.

NCERT Solutions for Class 8 Science Chapter 7 – 3 Mark Questions and Answers

Question 1.

1. What is Top soil ?
2. Mention two ways by which soil erosion can be prevented. [DA V (Winter) 2001]

Answer:

1. Top soil is the layer of soil contains rock particles, living organisms and humus.
2. Soil erosion can be prevented by :
   • Contour or step farming, which reduces the flow of water.
   • Planting trees as the roots help to bind the soil.

Question 2.
Mention two steps needed for conserving wildlife. Name two endangered species of animals.
Answer:
The following steps can be taken to conserve wildlife :

• by preserving the habitat of wildlife.
• by making hunting regulations and ensuring their effective implementation.

Bison and Beaver are two endangered species.

Question 3.
“When we conserve forests, we conserve wildlife and soil also”. Discuss. [DAV2002]
Answer:
Wildlife conservation is related to forest conservation. Man has cleared forests, converted grasslands into farmlands and flooded large areas by constructing dams. This has destroyed the habitat of the wildlife. Forests prevent soil erosion and maintain the fertility of the soil.

Question 4.
Explain three ways to conserve forests. [DAV2001]
Answer:
Three ways to conserve forests are : .

• Planned harvesting — cutting few trees at a time, so that the uncut trees prevent soil erosion and make seeds.
• Protection from fire.
• Protection from overgrazing by cattle, sheep, horses, etc.

Question 5.
How can the cutting of trees affect the ecological balance of a particular area ? [DAV (Winter) 1999]
Answer:
Cutting of trees :

• Disturbs the habitat of wild animals, which would lead to extinction of animal.
• Promotes soil erosion.
• More floods are caused
• Disturbs oxygen – carbon dioxide percentage.

Question 6.
Fill in the blanks

1. A place where animals are protected in their natural habitat is called …………
2. Species found only in a particular area is known as ……………
3. Migratory birds fly to far away places because of ………. changes

Answer:

1. Sanctuary
2. Endemic species
3. Climatic

Question 7.
What will happen if:

1.  we go on cutting trees.
2. the habitat of an animal is disturbed.
3. the top layer of the soil is exposed.

Answer:

1. If we go on cutting trees, rainfall and fertility of the soil will decrease. The chances of natural calamities such as floods and drought will increase. It will lead to decrease in the water holding capacity of the soil and movement of water from the soil surface into the ground. Animal life is also affected by deforestation.
2. If the habitat of an animal is disturbed, it endangers their existence. Survival of some animals becomes difficult because of the disturbances in their natural habitat.
3. Removal of the top layer of soil exposes the lower hard and rocky layers. This soil has less humus and it is less fertile. Gradually the fertile land can convert into deserts.

Question 8.
“Water is renewable but oil is not”. Explain.
Answer:
Water evaporates from forest and other vegetation and condenses in the upper layers of the atmosphere to form clouds and then it rains. The water goes down in the soil and is therefore, a renewable source.
Oil is found below the earth in crude form. It is formed after millions of years. When the oil is used, it is lost. Therefore, it is not a renewable source.

Question 9.
What is the difference in conservation of renewable and non-renewable resources ?
Answer:
Conserving of renewable resources is to utilise them in such a way that nature is able to replenish them as fast as they are used. In the case of non-renewable resources it is not so. These resources take a long time in their formation and will get finished very soon. So, they should be used judiciously.

NCERT Solutions for Class 8 Science Chapter 7 – 5 Mark Questions and Answers

Question 1.
Discuss the effects of deforestation on the following : [NCERT]

1. Wild animals.
2. Environment.
3. Villages (Rural areas).
4. Cities (Urban areas).
5. Earth.
6. The next generation.

Answer:

1. The natural habitat of wild animals is destroyed by deforestation.
2. Deforestation decreases the level of oxygen in the atmosphere and ground water level.
3. In the rural areas deforestation leads to loss in soil fertility and increased chances of natural calamities such as floods and drought.
4. Deforestation will lead to global warming in the cities.
5. On 4he whole earth, deforestation would lead to high temperatures and increased pollution level natural calamities and reduced levels of oxygen and ground water.
6. The next generation would not have enough wood and paper.

Question 2.
Answer in brief:

1. Why should we conserve biodiversity ?
2. Protected forests are also not completely safe for wild animals. Why ?
3. Some tribals depend on the jungle. How ?
4. What are the causes and consequences of deforestation ?
5. What is Red Data Book ?
6. What do you understand by the term migration ?

Answer:

1. Biodiversity is important for all living creatures for the preservation of environment and for economic reasons. Biodiversity is useful in scientific and medical research.
2. Protected forests are also not safe because people living in the neighbourhood encroach upon them and destroy them.
3. Many tribes still live in the jungle and are depend on the trees and the animals for their survival.
4. Causes of deforestation :
   • Using land for cultivation.
   • Building houses and factories.
   • Making furniture or using wood as a fuel.
   • Forest fires and severe drought.
5. Consequences of deforestation:
   • Increases the temperature and pollution level on the earth.
   • Decreases the level of oxygen in the atmosphere and lowers ground water level.
   • Increases chances of natural calamities.
   • Promotes soil erosion.
6. Migration means movement of the birds to far away specific areas every year during a particular time because of climatic changes.

Question 3.
List the methods by which non-renewable resources can be conserved.
Answer:
Non-renewable resources can be conserved by following methods :

1. Avoid wasteful use of sources.
2. Recycling resources e.g., paper, plastic bottles, etc.
3. Finding substitutes for non-renewable sources of energy, that is using alternative sources of energy such as solar energy, wind energy, etc.
4. Repair and use the appliance rather than discard it as soon as it gets spoilt.

Question 4.
“Conservation of resources means not only using the resources judiciously but also maintaining their quality”. Discuss.
Answer:
This statement is correct because if we have the resources of poor quality, it is of no use. We may have enough water, but if it is polluted it causes more harm than benefit. It causes many diseases in human beings and animals. Polluted air causes more harm in many cities as people get many diseases.

Question 5.
Why is managing of resources not very simple ?
Answer:
Managing resources is not very simple because the problems are inter related. Solving one problem leads to another problem. Banning of insecticides will save wildlife but will lead to shortage of food due to destruction of crops by insects. So, we can say that banning of one thing leads to shortage of another thing.

Question 6.

1. How does planting of trees help to conserve soil ?
2. Why should chemical fertilisers be used with caution ?

Answer:

1. The roots of trees helps to find the soil and prevent soil erosion. Rows of trees planted along the edges of farms act as wind breakers and prevent erosion by wind.
2. Chemical fertilisers damage the porous structure of the soil and also kill soil organisms such as earthworms which add loose fertile soil to the fields.

Question 7.

1. What are endemic species ? “
2. Why are these endemic species ?

Answer:

1. The species which are unique to a specific region are known as endemic species. Sal and wild mango are two example of endemic flora and bison and flying squirels are examples of endemic fauna.
2. These are endemic species because
   • their ecological requirements are met over a small area.
   • they are not capable of moving to other suitable habitats.

Question 8.

1. What are the five conservation categories of wildlife ?
2. How many biosphere reserves, national parks and sanctuaries are there in India ?

Answer:

1. There are five conservation categories of wildlife — extinct, endangered, vulnerable, rare and unsufficiently known species.
2. There are 15 biosphere reserves, 90 national parks and 448 sanctuaries in India

NCERT Solutions for Class 8 Science Chapter 7 MCQs

Question 1.
Conversion of fertile land into deserts is known as
(a) deforestation
(b) desertification
(c) conservation
(d) none of these.
Answer:
(b)

Question 2.
The variety of life on the earth is commonly referred to as
(a) biodiversity
(b) biosphere
(c) afforestation
(d) none of these.
Answer:
(a)

Question 3.
The first national park in India is
(a) Bandipur national park
(b) Kaziranga national park
(c) Jim Corbett national park
(d) Satpura national park.
Answer:
(c)

Question 4.
All type of plant life is known as
(a) fauna
(b) flora
(c) forest
(d) none of these.
Answer:
(b)

Question 5.
When no member of a species exists, it is known as
(a) endemic species
(b) endangered species
(c) extinct
(d) vulnerable species.
Answer:
(c)

Question 6.
Snow leopard is
(a) vulnerable species
(b) endangered species
(c) extinct
(d) endemic species.
Answer:
(b)

Question 7.
A species found only in one particular place is known as
(a) endemic
(b) vulnerable
(c) endangered
(d) extinct.
Answer:
(a)

Question 8.
Migration of birds takes place because
(a) they like to travel
(b) to find abundant food
(c) to meet other birds
(d) none of these.
Answer:
(b)

Question 9.
Growing new trees in forests is known as
(a) deforestation
(b) desertification
(c) afforestation
(d) none of these.
Answer:
(c)

Question 10.
How many Biosphere Reserves in India has the Indian Government established ?
(a) 10
(b) 5
(c) 14
(d) 20
Answer:
(c)

Combustion and Flame Class 8 Science NCERT Textbook Questions

Question 1.
List conditions under which combustion can take place.
Answer:
Combustion can take place in the presence of:
(a) a combustible substance.
(b) oxygen, that is, the supporter of combustion.
(c) attainment of ignition temperature of the substance.

Question 2.
Fill in the blanks.
(a) Burning of wood and coal causes _____ of air.
(b) A liquid fuel, used in homes is ______
(c) Fuel must be heated to its ______ before it starts burning.
(d) Fire produced by oil cannot be controlled by ______
Answer:
(a) pollution
(b) LPG
(c) ignition temperature
(d) water

Question 3.
Explain how the use of CNG in automobiles has reduced pollution in our cities.
Answer:
The use of CNG in automobiles has reduced pollution in our cities as it is a quality fuel and has some benefits:
(a) It gives out less carbon dioxide gas, carbon monoxide gas, sulphur dioxide and nitrogen dioxide, which is beneficial as they play crucial role in global warming and acid rain.
(b) It leaves behind no residue after its combustion.

Question 4.
Compare LPG and wood as fuels.
Answer:

LPG	Wood
(i) It does not cause pollution on combustion.	(i) It pollutes air on its combustion.
(ii) No smoke is produced.	(ii) It produces smoke.
(iii) It is a liquid fuel.	(iii) It is a solid fuel.
(iv) It has more calorific value (55000 kJ/kg).	(iv) It has less calorific value (17000 kJ/kg).
(v) It can be easily transported, as it is stored in cylinders.	(v) It can’t be transported easily like LPG fuels.

Question 5.
Give reasons.
(a) Water is not used to control fires involving electrical equipment.
(b) LPG is a better domestic fuel than wood.
(c) Paper by itself catches fire easily whereas a piece of paper wrapped around an aluminium pipe does not.
Answer:
(a) Since water is a good conductor of electricity, it may result in electric shocks to the person trying to extinguish fire.
(b) LPG is better domestic fuel than wood because it does not produce gases, nor does it leave any residue behind. Moreover, it has more calorific value than wood.
(c) As its ignition temperature is low, the paper by itself catches fire easily. But a piece of paper wrapped around an aluminium pipe does not catch fire easily, as the heat being given gets absorbed by the aluminium pipe and the piece of paper does not get its ignition temperature.

Question 6.
Make a labelled diagram of a candle flame.
Answer:

Question 7.
Name the unit in which the calorific value of a fuel is expressed.
Answer:
The unit in which the calorific value of a fuel is expressed is kilojoules per kilogram (kJ/kg).

Question 8.
Explain how CO2 is able to control fires.
Answer:
As CO2 is heavier than oxygen, it forms a blanket around fire, because of which the supply of air is stopped. Men over, it brings down the temperature of the burning substance. In these ways, it plays a significant role in controlling fire.

Question 9.
It is difficult to burn a heap of green leaves but dry leaves catch fire easily. Explain.
Answer:
The green leaves hold some amount of water, so its ignition temperature gets increased and it does not burn easily. On the other hand, dry leaves are waterless, so they catch fire easily (having low ignition temperature).

Question 10.
Which zone of a flame does a goldsmith use for melting gold and silver and why?
Answer:
A goldsmith uses the outermost zone of a flame, which is non-luminous, to melt gold and silver as it is the hottest zone of the flame, having more temperature.

Question 11.
In an experiment, 4.5 kg of a fuel was completely burnt. The heat produced was measured to be 180,000 kJ. Calculate the calorific value of the fuel.
Answer:
Calorific value of a fuel = HeatProducedAmountoffuel
= 1800004.5 kJ/kg
= 40,000 kJ/kg.

Question 12.
Can the process of rusting be called combustion? Discuss.
Answer:
The process of rusting emits heat during the formation of its oxide. So we can call the process of rusting as slow combustion.

Question 13.
Abida and Ramesh were doing an experiment in which water was to be heated in a beaker. Abida kept the beaker near the wick in the yellow part of the candle flame. Ramesh kept the beaker in the outermost part of the flame. Whose water will get heated in a shorter time?
Answer:
The water which was put by Ramesh will get heated in a shorter time; because he had put it nearer to the hottest zone of the flame.

Combustion and Flame Class 8 Science NCERT Intext Activities Solved

Activity 1
Collect some materials like straw, matchsticks, kerosene oil, paper, iron nails,^ stone pieces, glass, etc. Under the supervision of your teacher try to burn each of these materials one by one. If combustion takes place mark the material combustible, otherwise mark it non-combustible (Table 6.1).
Solution:
Combustible and Non-combustible Substances

Material	Combustible	Non-combustible
Wood	✓
Paper	✓
Iron nails		✓
Kerosene oil	✓
Stone piece		✓
Straw	✓
Charcoal	✓
Matchsticks	✓
Glass		✓

Activity 2

(Caution: Be careful while handling burning candle).
Fix a lighted candle on a table. Put a glass chimney over the candle and rest it on a few wooden blocks in such a way that air can enter the chimney [Fig. 6;3(a)]. Observe what happens to the flame. Now remove the blocks and let the chimney rest on the table [Fig. 6.3(b)]. Again observe the flame. Finally, put a glass plate over the chimney [Fig. 6.3(c)]. Watch the flame again. What happens in the three cases? Does the flame flicker off? Does it flicker and give smoke? Does it burn unaffected? Can you infer anything at all about the role played by air in the process of burning?

Solution:
The candle burns freely in case (a) when air can enter the chimney from below. In case (b), when air does not I enter the chimney from below, the flame flickers and produces smoke. In case (c), the flame finally goes off because the air is not available.

Activity 3
Place a piece of burning wood or charcoal on an iron plate or Tawa. Cover it with a glass jar or a tumbler, or a transparent plastic jar. Observe what happens. Does charcoal stop burning after sometime? Can you think of a reason why it stops burning?
Solution:
After burning under the jar for some time, the wood/charcoal stops burning due to the discontinuous supply of air (or oxygen present in the air).

Activity 4

(Caution: Be careful while handling burning candle)
Make two paper cups by folding a sheet of paper. Pour about 50 ml. of water in one of the cups. Heat both the cups separately with a candle (Fig. 6.4). What do you observe?

Solution:
It is observed that the empty cup catches fire immediately and begins to burn, whereas the cup containing water does not burn; instead, the water present in it becomes hot.

Activity 5

Light a candle (Caution: Be careful). Hold a glass tube with a pair of tongs and introduce its one end in the dark zone of a non-flickering candle flame (Fig. 6.5). Bring a lighted matchstick near the other end of the glass tube. Do you see a flame? If so, what is it that produces a flame?

Solution:
When we bring a lighted matchstick near the other end of the glass tube then we observe a flame. The vapourised wax from candle produces this flame.

NCERT Solutions for Class 8 Science Chapter 6 – 1 Mark Questions and Answers

Question 1.
An important liquid fuel, used in home is ……….. [KVS 2008]
Answer:
Kerosene

Question 2.
What are the main constituent of biogas and kitchen gas (L.P.G.) ? [NCT 2005]
Answer:
The main constituent of biogas is methane and of kitchen gas (L.P.G.) is butane.

Question 3.
What is biogas ? [KVS 2005]
Answer:
Biogas is formed by the decomposition of plant and animal wastes.

Question 4.
Fuel must be heated to its ……….. temperature before it starts burning. [KVS 2005]
Answer:
Fuel must be heated to its ignition temperature before it starts burning.

Question 5.
……….. is a liquid fuel.
Answer:
Petrol is a liquid fuel.

Question 6.
When fuels bum what do they produce ?
Answer:
They produce heat and light.

Question 7.
List conditions under which combustion can take place. [NCERT]
Answer:
The conditions under which combustion can take place :

• Presence of combustible substance.
• Presence of supporter of combustion i.e., oxygen.
• Attainment of ignition temperature

Question 8.
Define combustion.
Answer:
Combustion is the process of burning of substances to give heat and light.

Question 9.
What name is given to the substances which can bum easily ?
Answer:
Combustible substances.

Question 10.
Give two examples of the combustible substances.
Answer:
Kerosene oil and wood.

Question 11.
What name is given to the substances which do not bum ?
Answer:
Non-combustible substances.

Question 12.
Classify the following as combustible and non-combustible substances- Paper, iron nails, cloth, glass.
Answer:
Combustible substances – paper, cloth.
Non-combustible substances – iron, nails, glass.

Question 13.
How is heat and light produced in the sun ?
Answer:
In the sun, heat and light are produced by nuclear fusion actions.

Question 14.
When does a substance start burning ?
Answer:
A substance starts burning when its ignition temperature is reached.

Question 15.
Give two examples of inflammable substances.
Answer:
Petrol and LPG.

NCERT Solutions for Class 8 Science Chapter 6 – 2 Mark Questions and Answers

Question 1.
Abida and Ramesh were doing an experiment in which water was to be heated in a beaker. Abida kept the beaker near the wick in the yellow part of the candle flame. Ramesh kept the beaker in the outermost part of the flame. Whose water will get heated in a shorter time ? Why? [NCERT]
Answer:
Ramesh’s water will get heated faster because it is kept in the outermost zone of the flame which is hottest part of flame.

Question 2.
Explain how CO2 is able to control fires. [NCERT]
Answer:
Carbon dioxide is used for extinguishing fire because it is a non-supporter of combustion and is non-combustible. Also it is heavier than air and settles on the fire.

Question 3.
What is a fuel ? Name two liquid fuels.
Answer:
A substance which on burning produces heat energy is called a fuel. Kerosene and petrol are liquid fuels.

Question 4.
Is the food a fuel for our body ?
Answer:
Yes, in our body food is broken down by reaction with oxygen and heat is produced.

Question 5.
Distinguish between combustible and non-combustible substances.
Answer:
Combustible substances : The substances which bum easily are called combustible substances, e.g., paper, cloth.
Non-combustible substances : The substances which do not bum easily are called Non-combustible substances, e.g., iron, glass.

Question 6.
Can you bum paper when a burning matchstick is brought near it ? Why ?
Answer:
A paper can be burnt with a burning matchstick because of its low ignition temperature.

Question 7.
What is forest fire ?
Answer:
During extreme heat of summer, at some places dry grasses catch fire. This fire then spreads to trees and the whole forest is on fire.

Question 8.
Why do different substances catch fire at different temperatures ?
Answer:
Different substances catch fire at different temperatures because they have different ignition temperatures.

Question 9.
Kerosene oil catches fire faster than wood. Why ?
Answer:
The ignition temperature of kerosene is lower than that of wood, so it bums quickly

Question 10.
Why is water poured to extinguish burning wood ?
Answer:
When water is poured on burning wood, the temperature of wood falls below its ignition temperature. This prevents fire from spreading.

NCERT Solutions for Class 8 Science Chapter 6 – 3 Mark Questions and Answers

Question 1.

1. Name the type of nuclear reaction taking place in the atmosphere of Sun.
2. Define ignition temperature.
3. Why water should not be used to put out fire caused by burning of petrol. [MSE (Chandigarh) 2008]

Answer:

1. Nuclear fusion.
2. The minimum temperature to which a substance is heated before it starts burning is known as ignition temperature.
3. Petrol is lighter than water, so it floats on top of water and continuous burning. So, it cannot be used for extinguishing fire due to burning of petrol.

Question 2.
Give two examples each of solid fuel, liquid fuel and gaseous fuel. [KVS 2008]
Answer:

• Solid fuel — coal, wood
• Liquid fuel — petrol, kerosene
• Gaseous fiiel — LPG, methane

Question 3.
Write any four characteristics of an ideal fuel. What is C.N.G. ? Mention its one use. [DAV2005]
Answer:

• It is cheap and easily available. ,
• It does not produce any harmful gas during burning.
• It has high calorific value.
• It is safe and easy to store.

C.N.G – Compressed Natural Gas. It is used as a fuel for automobiles.

Question 4.
Explain the different zones of a flame with the help of a neat and well labelled diagram.
Answer:

• The innermost zone is the dark zone. It contains unbumt vapours of wax.
• The second zone is the yellow zone where incomplete combustion takes place. It is known as luminous zone.
• The thin outermost zone of the flame is blue in colour and complete combustion takes place. This is the non-luminous zone.
  

Question 5.

1. Which is the hottest zone and the coolest zone of a flame ?
2. Why does the middle zone of the candle flame glow with yellow colour ?

Answer:

1. The innermost or dark zone has minimum temperature. The outermost or non-luminous zone has maximum temperature.
2. In the middle zone, the unbumt carbon particles give the flame its yellow colour.

Question 6.
Why do we use paper or kerosene oil to start fire in wood or coal ?
Answer:
The ignition temperature of wood or coal is very high. So, we bum paper or kerosene oil to provide large amount of heat, as they have a low ignition temperature.

Question 7.
Explain how water extinguishes the fire.
Answer:
Water cools the combustible material so that its temperature is brought below its ignition temperature. Water vapours also surround the combustible material, helping in cutting the supply of air. So, the fire is extinguished.

Question 8.
How does the foam type fire extinguisher work ?
Answer:
At airports and petrol pumps, the foam type fire extinguisher is used which is based on the principle of smothering the fire. In this extinguisher, sodium bicarbonate contains Turkey red oil. When it is operated, carbon dioxide liberated in reaction of dilute sulphuric acid with sodium bicarbonate comes out under pressure in the form of a foam and settles on the fire.

Question 9.
You are given three substances A, B and C. How will you find out which of them as a combustible material ?
Answer:
He will bum each substance with the help of math stick. If it bums it is a combustible substance and if it doesnot bum it is a non-combustible substance.

Question 10.
When the clothes of a person catches fire, we cover him with a blanket. Why ?
Answer:
When the person is covered with a blanket, the supply of oxygen is cut off. So, the fire is put off.

NCERT Solutions for Class 8 Science Chapter 6 – 5 Mark Questions and Answers

Question 1.

1. What is a fuel ?
2. Define calorific value of a fuel. [DAV1997]
3. Give the characteristics of a good fuel.

Answer:

1. A fuel is a substance which gives heat on burning.
2. Calorific value is the amount of heat energy produced on complete combustion of 1 kg of fuel. It is expressed as KJ/Kg.
3. Characteristics of a good fuel are –
   • It should have high calorific value.
   • It should not leave ash behind.
   • It should be easy to store, transport and handle.
   • It should have convenient ignition temperature.

Question 2.
Fill in the blanks : [NCERT]

1. Burning of wood and coal causes ………. of air.
2. A liquid fuel, used in homes is ……….
3. Fuel must be heated to its ……….. before it starts burning.
4. Fire produced by oil cannot be controlled by ……………

Answer:

1. pollution
2. kerosene
3. ignition temperature
4. water.

Question 3.
Explain how the use of CNG in automobiles has reduced pollution in our cities. [NCERT]
Answer:
CNG produces no pollutants like carbon dioxide, carbon monoxide, unbumt carbon particles and sulphur dioxide. Therefore, it has reduced pollution in our cities.

Question 4.
Give reasons. [NCERT]

1. Water is not used to control fires involving electrical equipment.
2. LPG is a better domestic fuel than wood.
3. Paper by itself catches fire easily whereas a piece of paper wrapped around an aluminium pipe does not.

Answer:

1. Water is not used to control the fire involving electrical equipment because it is a good conductor of electricity. The person using it can get a shock.
2. LPG is a better domestic fuel than wood because
   • It does not give out smoke.
   • It has high heat content.
   • It does not leave ash behind.
   • It is easily available.
3. Paper by itself catches fire easily because it is a highly combustible substance. But when it is wrapped on aluminium, it does not bum because aluminium is a good conductor of heat and it takes the heat from paper.

Question 5.
It is difficult to bum a heap of green leaves but dry leaves catch fire easily. Explain. [NCERT]
Answer:
Green leaves contain moisture, so they do not catch fire. Dry leaves do not contain moisture, so they catch fire easily. Moisture increases the ignition temperature of leaves.

Question 6.
In an experiment 4.5 kg of a fuel was completely burnt. The heat produced Was measured to be 1,80,000 kJ. Calculate the calorific value of the fuel. [NCERT]
Answer:
Heat produced = 180,000kJ
Mass of fuel = 4.5 kg
Calorific value = 180,000 kJ/4.5 kg = 40,000 kJ/kg.

Question 7.
Can the process of rusting be called combustion ? Discuss. [NCERT]
Answer:
Rusting is an oxidation process but it cannot be called combustion because heat and light are not produced.

Question 8.
Compare LPG and wood as fuels. [NCERT]
Answer:
LPG is a better domestic fuel than wood because

• It does not give out smoke.
• It has high heat content.
• It does not leave ash behind.
• It is easily available.

Question 9.
Give some effects of fuels combustion.
Answer:

• Carbon fuels release unbumt carbon particles and cause asthma.
• Incomplete combustion forms carbon monoxide which is a poisonous gas.
• Combustion of fuels releases carbon dioxide which causes global warming.
• Increased use of fuel causes acid rain which harm crops, buildings and soil.

Question 10.
Why is wood used as a fuel in villages ? What are the disadvantages of using wood as a fuel ?
Answer:
In villages wood is used because it is easily available and cheap.
Its disadvantages are:

• It produces lot of smoke which causes respiratory problems.
• Wood contains several important substances which are lost when it is burnt,
• Cutting of trees leads to deforestation.

NCERT Solutions for Class 8 Science Chapter 6 MCQs

Question 1.
The gas required for combustion is [NCERT]
(a) oxygen
(b) nitrogen
(c) carbon dioxide
(d) hydrogen
Answer:
(a)

Question 2.
Burning of hydrogen is an example of
(a) slow combustion
(b) rapid combustion
(c) explosion
(d) spontaneous combustion
Answer:
(c)

Question 3.
The gas produced in the working of soda-acid type fire extinguisher is
(a) carbon dioxide
(b) oxygen
(c) sulphur dioxide
(d) hydrogen
Answer:
(a)

Question 4.
The fuel used in the human body to produce energy, is
(a) coal
(b) food
(c) juices
(d) paper
Answer:
(b)

Question 5.
Burning of LPG at home is an example of
(a) slow combustion
(b) rapid combustion
(c) spontaneous combustion
(d) explosion
Answer:
(b)

Question 6.
Which one of the following will show spontaneous combustion?
(a) Sodium
(b) Calcium
(c) Sulphur
(d) Carbon
Answer:
(a)

Question 7.
Which of the following can be used to extinguish fire at the petrol pump ?
(a) Water
(b) Carbon dioxide
(c) Blanket
(d) None of these
Answer:
(b)

Question 8.
While shaping gold into ornaments, which part of the flame directly used by goldsmith?
(a) Non-luminous
(b) Luminous
(c) Innermost zone
(d) Whole flame
Answer:
(a)

Question 9.
Which fuel is the ideal fuel to be used at home ?
(a) LPG
(b) CNG
(c) Wood
(d) Coal
Answer:
(a)

Coal and Petroleum Class 8 Science NCERT Textbook Questions

Question 1.
What are the advantages of using CNG and LPG as fuels?
Answer:
The advantages of using CNG and LPG as fuels are:

• They burn with a smokeless flame and so does not cause any pollution.
• They leave no ash on burning.
• They are easy to handle and convenient to store.

Question 2.
Name the petroleum product used for surfacing of roads.
Answer:
Bitumen

Question 3.
Describe how coal is formed from dead vegetation. What is this process called?
Answer:
Millions of years ago, trees, plants, ferns and forests got buried below the rocks, soil and sand due to natural processes like flooding, earthquake, etc. Slowly, as more soil deposited over them, they were compressed. This led to the conditions of high pressure and heat. These conditions along with the anaerobic conditions turned the carbon-enriched organic matter of wood into coal.
This slow process of conversion of wood into coal is called carbonisation.

Question 4.
Fill in the blanks.
(a) Fossils fuels are ____ , ____ and ____
(b) Process of separation of different constituents from petroleum is called ______
(c) Least polluting fuel for vehicle is ______
Answer:
(a) coal, petroleum, natural gas
(b) refining
(c) CNG

Question 5.
Tick True/False against the following statements.
(a) Fossil fuels can be made in the laboratory.
(b) CNG is more polluting fuel than petrol.
(c) Coke is an almost pure form of carbon.
(d) Coal tar is a mixture of various substances.
(e) Kerosene is not a fossil fuel.
Answer:
(a) False
(b) False
(c) True
(d) True
(e) False

Question 6.
Explain why fossil fuels are exhaustible natural resources.
Answer:
Fossil fuels take millions of years to be formed. They are limited in nature and cannot be replenished easily, once consumed. Hence, they are considered as exhaustible natural resources.

Question 7.
Describe the characteristics and uses of coke.
Answer:
Characteristics of coke: Coke is 98% pure carbon. It is a tough, porous and black substance. It pro-duces a very little smoke.
Uses of coke: Coke is very useful as fuel. It is a good reducing agent. It is widely used in metallurgical processes to reduce metals from their oxides. It is used for producing water gas.

Question 8.
Explain the process of the formation of petroleum.
Answer:
Petroleum is formed by the burial of aquatic plants and animals below the sea bed. The marine animals and plants died thousands of years ago and settled down in the bottom of sea. In anaerobic conditions, microorganisms decompose this organic matter. Due to high pressure and heat, the dead remains of tiny plants and animals were slowly converted into petroleum.

Question 9.
The following table shows the total power shortage in India from 2004-2010. Show the data in the form of a graph. Piet shortage percentage for the years on the y-axis and the year on the x-axis.

S. No.	Year	Shortage (%)
1	2004	7.8
2	2005	8.6
3	2006	9.0
4	2007	9.5
5	2008	9.9
6	2009	11.2
7	2010	10.0

Answer:

Coal and Petroleum Class 8 Science NCERT Intext Activities Solved

Activity 1

Make a list of various materials used by us in daily life and classify them as natural and man-made.
Solution:

Natural	Man-made
Air	Clothes
Sunlight	Plastics
Water	Fan
Minerals	Cement
Forests	Cosmetics

Activity 2
Take some containers. Fill them with popcorn/peanuts/roasted gram/tof¬fees. Divide students into groups of seven each. Further divide each group into three subgroups containing 1, 2 and 4 students. Label them as first, second and third generation respectively.
These sub-groups represent the consumers. As population is growing, second and third generations have larger number of consumers.
Put one full container for each group on a table. Ask consumers of the first generation from each group to consume eatables from the container of their group. Now, ask the second generation consumers from each group to do the same. Ask students to observe carefully the availability of eatables in each container. If something is left in the containers, ask third generation from each group to consume it. Now, finally observe whether all the consumers of the third generation got the eatables or not. Also observe if anything is still left in any of the containers.
Solution:
Students should perform this activity themselves in their classroom.

NCERT Solutions for Class 8 Science Chapter 5 – 1 Mark Questions and Answers

Question 1.
Name the petroleum product used for surfacing of roads. [NCERT]
Answer:
Bitumen.

Question 2.
What is the slow process of conversion of dead vegetation into coal called ?
Answer:
Carbonisation.

Question 3.
Fill in the blanks : [NCERT]

• Fossil fuels are ……, ……. and ……..
• Process of separation of different constituents from petroleum is called ………
• Least polluting fuel for vehicle is ………..

Answer:

• coal, petroleum, natural gas
• refining
• CNG.

Question 4.
Tick True/False against the following statements : [NCERT]

1. Fossil fuels can be made in the laboratory. (T/F)
2. CNG is more polluting fuel than petrol. (T/F)
3. Coke is almost pure form of carbon. (T/F)
4. Coal tar is a mixture of various substances. (T/F)
5. Kerosene is not a fossil fuel. (T/F)

Answer:

1. False
2. False
3. True
4. True
5. False

Question 5.
Explain why fossil fuels are exhaustible natural resources. [NCERT]
Answer:
Fossil fuels are exhaustible natural resources because they will be exhausted by human activities as they are limited in nature.

Question 6.
What are natural resources ?
Answer:
Material obtained from nature are called natural resources.

Question 7.
Classify the following as exhaustible and inexhaustible natural resources- air, sunlight, water, forests, wildlife, coal.
Answer:
Exhaustible resources – forests, wildlife, coal
Inexhaustible resources – air, sunlight, water.

Question 8.
Define carbonisation.
Answer:
The slow process of conversion of dead vegetation into coal is called carbonisation.

Question 9.
What name is given to the process of heating a substance in absence of air ?
Answer:
Destructive Distillation.

Question 10.
How is coke obtained ?
Answer:
Coke is obtained by heating coal in the absence of air.

Question 11.
How is coal tar formed ?
Answer:
When destructive distillation of coal is done, the vapours which condense in the water form coal tar.

Question 12.
Why is petroleum called a fossil fuel ?
Answer:
Petroleum is called a fossil fuel as it is obtained from the bodies of dead organisms.

Question 13.
How is natural gas formed ?
Answer:
Natural gas is formed below the earth’s surface. It is formed above the petroleum.

NCERT Solutions for Class 8 Science Chapter 5 – 2 Mark Questions and Answers

Question 1.
Write down any four amorphous forms of carbon. [KVS 2008]
Answer:
Amorphous forms of carbon – coal, charcoal, coke and lamp black.

Question 2.
Explain the process of formation of petroleum ? Name two places in India where it is found.
Answer:
Petroleum is formed by the decomposition of aquatic plants and animal remains. In India, petroleum is obtained from oil wells in Assam and Bombay High.

Question 3.
Distinguish between inexhaustible and exhaustible natural resources.
Answer:
Exhaustible resources – forests, wildlife, coal
Inexhaustible resources – air, sunlight, water.

Question 4.
Why are coal and petroleum known as fossil fuels ?
Answer:
Coal and petroleum are formed from the dead remains of living organisms that is why they are called fossils fuels.

Question 5.
Give two characteristics of coal.
Answer:
Coal is hard and is of black in colour.

Question 6.
Define destructive distillation. Name the residue formed by destructive distillation of coal.
Answer:
Destructive distillation is the process of heating a substance in absence of air. Coke is formed by destructive distillation of coal.

Question 7.
What is meant by refining of petroleum and where is it done ?
Answer:
The process of separating the different fractions of petroleum is known as refining and it is carried out in a refinery.

Question 8.
Give two uses of diesel.
Answer:
Diesel is used as fuel for heavy motor vehicles and in electric generators.

Question 9.
How can petrol be used ?
Answer:
Petrol can be used as a motor fuel, aviation fuel and as solvent for dry cleaning.

Question 10.
How can bitumen be used ?
Answer:
Bitumen can be used for making paints and for surfacing the roads.

Question 11.
Why is petroleum also knbwn as ‘black gold’ ?
Answer:
Due to its great commercial importance, petroleum is known as ‘black gold’.

Question 12.
Can we make coal and petroleum in the laboratory from dead organisms ?
Answer:
No, their formation is a very slow process and conditions for their formation cannot be reached in the laboratory.

Question 13.
Give two disadvantages of using fossil fuels.
Answer:
Fossil fuels cause air pollution and global warming.

Question 14.
Why should the fossil fuels be used with care ?
Answer:
If we use fossil fuels carefully, it will result in better environment, less risk of global warming and they will be available for a longer period.

Question 15.
What is meant by fractional distillation ? What is the principle on which it is based ?
Answer:
Petroleum is mixture of various hydrocarbons having different boiling points. As the number of carbon atoms increase, the boiling point also increases. This property is used to separate the different components of petroleum and is known as fractional distillation.

NCERT Solutions for Class 8 Science Chapter 5 – 3 Mark Questions and Answers

Question 1.
Define the term fossil fuel. Name two fossil fuels. [KVS 2008, 2005]
Answer:
Fossil fuels are formed from dead remains of living matter over millions of years when they remained buried under the earth. Coal and petroleum are two fossil fuels.

Question 2.
State one use of each of the following : [KVS 2007]

• Charcoal
• Bone Charcoal
• Coke.

Answer:
Use:

• Charcoal : Fuel.
• Bone Charcoal : Purification of brown coloured sugarcane juice in the manufacture of sugar.
• Coke : Used as a reducing agent in the extraction of metals.

Question 3.

1. Name the products obtained when coal is heated in the absence of air.
2. Write any two uses of its products. [MSE (Chandigarh) 2007]

Answer:

1. Coke is formed when coal is heated in absence of air.
2. Coke is used :
   • As a fuel.
   • As a reducing agent in the extraction of metals.

Question 4.
(a) Give the full form of
(i) LPG
(ii) CNG.
(b) How is petroleum gas obtained ? [MSE (Chandigarh) 2007]
Answer:
(a) (i) LPG — Liquefied Petroleum Gas.
(ii) CNG — Compressed Natural Gas.
(b) Petroleum gas is obtained during fractional distillation of petroleum.

Question 5.
Draw diagram to show petroleum and natural gas deposit.
Answer:

Question 6.
What are ‘Petrochemicals’ ? Give the uses of petrochemicals obtained from petroleum.
Answer:
Petrochemicals are useful substances obtained from petroleum. They are used in the manufacture of detergents, fibres, polyethylene and other plastics.

Question 7.
Name some places where natural gas is found in India. How many reserves are of natural gas ?
Answer:
In India, natural gas has been formed in Tripura, in the Krishna Godavari delta. In India, there are over 100 billion cubic metre reserves of natural gas.

Question 8.
Describe characteristics and uses of coke.
Answer:
Characteristics of coke are :

• it is tough.
• it is porous
• it is pure form of carbon.

Coke is used for extraction of metals and in the manufacture of steel.

NCERT Solutions for Class 8 Science Chapter 5 – 5 Mark Questions and Answers

Question 1.

1. What is CNG ? Give its one use.
2. From which natural substance are liquid fuels formed ?
3. Which gas is the main constituent of LPG ?
4. How was petroleum formed in nature ?
5. Why do green leaves not catch fire easily ? [DAV2007]

Answer:

1. CNG — Compressed Natural Gas. It is used as a fuel.
2. All liquid fuels are formed from petroleum.
3. Butane is the main constituent of LPG.
4. Petroleum was formed by the sedimentation of dead remains of microscopic marine plants and animals, which were buried under the surface of the earth, millions of years ago.
5. Green leaves do not catch fire easily because they contain moisture.

Question 2.

1. How have fossil fuels been formed ?
2. Why are fossil fuels non-renewable sources of energy ?
3. Why is smelling agent added to LPG ?
4. Give one reason why LPG is a better fuel than coal.
5. Give one advantage of modem chullah over traditional chullah. [DAV 2006]

Answer:

1. They have been formed by decomposition of pre-historic plants and animals buried under the Earth’s crust millions of years ago.
2. Fossil fuels are non-renewable sources of energy because once exhausted they cannot be re-created in a short period of time.
3. Smelling agent is added to LPG to detect the leakage of gas as LPG is colourless and odourless gas.
4. LPG is a better fuel than coal because :
   • It does not cause pollution.
   • It has high calorific value.
   • It has low ignition temperature. (Any one)
5. Advantages of Modem Chullah over Traditional Chullah :
   • High efficiency.
   • Causes less pollution.
   • Consumes less fuel.

Question 3.
The following table shows the total power shortage in India from 1991-1997. Show the data in the form of a graph. Plot shortage percentage for the years on Y-axis and the year on the X-axis. [NCERT]

S. No.	Year	Shortage (% age)
1	1991	7.9
2	1992	7.8
3	1993	8.3
4	1994	7.4
5	1995	7.1
6	1996	9.2
7	1997	11.5

Answer:

Question 4.
Name the agency in India who advises people how to save petrol/diesel. What tips are given by them ?
Answer:
In India, the Petroleum Conservation Research Association (PCRA) advises people how to save petrol/diesel while driving.
Their tips are :

• Drive at a constant and moderate speed.
• Switch off the engine at traffic lights.
• Ensure correct tyre pressure.
• Ensure regular maintenance of the vehicle.

Question 5.
Draw a labelled diagram showing the fractional distillation of petroleum. Give the uses of any three fractions.
Answer:

Uses:

• Petrol is used as motor fuel, airation fuel and as solvent for drycleaning.
• Kerosene is used as fuel at home and in jet aircrafts.
• Diesel is used as fuel for heavy motor vehicles and electric generators.

NCERT Solutions for Class 8 Science Chapter 5 MCQs

Question 1.
Wind, sun and hydropower are
(a) renewable
(b) non-renewable
(c) synthetic sources
(d) none of these .
Answer:
(a)

Question 2.
The unit of calorific value of combustion of fuels is
(a) kilojoule
(b) joule
(c) kilojoule/kilogram
(d) kilogram
Answer:
(c)

Question 3.
A brownish-black sedimentary rock is known as
(a) charcoal
(b) coke
(c) coal
(d) coal tar
Answer:
(c)

Question 4.
Peat is a type of
(a) charcoal
(b) coke
(c) coal
(d) none of these
Answer:
(c)

Question 5.
The most pure form of carbon fuel is
(a) coal
(b) coke
(c) charcoal
(d) coal gas
Answer:
(b)

Question 6.
The fossil fuel found below the sea is
(a) petrol
(b) petroleum
(c) kerosene
(d) diesel
Answer:
(b)

Question 7.
‘Black gold’ is another name for
(a) coal
(b) coke
(c) charcoal
(d) petroleum
Answer:
(d)

Question 8.
The white semi-solid fraction of petroleum used for making vaseline is
(a) asphalt
(b) lubricating oil
(c) paraffin wax
(d) fuel oil
Answer:
(c)

Question 9.
Out of the following, which fuel is best used in the homes ?
(a) Wood
(b) CNG
(c) LPG
(d) Kerosene oil
Answer:
(c)

Materials: Metals and Non-Metals Class 8 Science NCERT Textbook Questions

Question 1.
Which of the following can be beaten into thin sheets?
(a) Zinc
(b) Phosphorus
(c) Sulphur
(d) Oxygen
Answer:
(a) Zinc

Question 2.
Which of the following statements is correct?
(a) All metals are ductile.
(b) All non-metals are ductile.
(c) Generally, metals are ductile.
(d) Some non-metals are ductile.
Answer:
(c) Generally, metals are ductile

Question 3.
Fill in the blanks.
(a) Phosphorus is a very ____ non-metal.
(b) Metals are _____ conductors of heat and _____
(c) Iron is ______ reactive than copper.
(d) Metals react with acids to produce ______ gas.
Answer:
(a) reactive
(b) good, electricity
(c) more
(d) hydrogen

Question 4.
Mark ‘T’ if the statement is true and ‘F’ if it is false.
(a) Generally, non-metals react with acids.
(b) Sodium is a very reactive metal.
(c) Copper displaces zinc from zinc sulphate solution.
(d) Coal can be drawn into wires.
Answer:
(a) False
(b) True
(c) False
(d) False

Question 5.
Some properties are listed in the following Table. Distinguish between metals and non-metals on the basis of these properties.

Properties	Metals	Non-metals
1. Appearance
2. Hardness
3. Malleability
4. Ductility
5. Heat Conduction
6. Conduction of Electricity

Answer:

Properties	Metals	Non-metals
1. Appearance	have metallic lustre	dull
2. Hardness	hard	soft
3. Malleability	malleable	non-malleable
4. Ductility	ductile	non-ductile
5. Heat Conduction	good conductors	bad conductors
6. Conduction of Electricity	good conductors	bad conductors/insulators

Question 6.
Give reasons for the following.
(a) Aluminium foils are used to wrap food items.
(b) Immersion rods for heating liquids are made up of metallic substances.
(c) Copper cannot displace zinc from its salt solution.
(d) Sodium and potassium are stored in kerosene.
Answer:
(a) Aluminium is highly malleable and it can be easily beaten in sheets to make its foil for wrapping purposes. It is also soft and does not react with food items. That is why aluminium foils are used . to wrap food items.
(b) Immersion rods made up of metallic substances because metals are good conductors of heat and electricity. They get hot very soon on the passage of electric current and warm the water.
(c) Copper is less reactive than zinc. So it cannot displace zinc from its solution.
(d) Sodium and potassium are highly reactive, so they are stored in kerosene.

Question 7.
Can you store the lemon pickle in an aluminium utensil? Explain.
Answer:
No, we cannot store lemon pickle in an aluminium utensil because aluminium is a metal and metals readily react with acids to produce hydrogen. When aluminium comes in contact with lemon, which is acidic, would react to give hydrogen and the pickles will be spoiled.

Question 8.
Match the substances given in column A with their uses given in column B.

A	B
Gold	Thermometers
Iron	Electric wire
Aluminium	Wrapping food
Carbon	Jewellery
Copper	Machinery
Mercury	Fuel

Answer:
(i) (d)
(ii) (e)
(iii) (c)
(iv) (f)
(v) (b)
(vi) (a)

Question 9.
What happens when
(a) Dilute sulphuric acid is poured on a copper plate?
(b) Iron nails are placed in a copper sulphate solution?
Write word equations of the reactions involved.
Answer:
(a) No reaction will take place because copper is very less reactive.
(b) Iron being more reactive than copper will replace copper from its solution and brown coating of copper is deposited on the iron nails. Also, the blue colour turns green.
Iron + Copper sulphate (solution) → Iron sulphate (solution) + Copper

Question 10.
Saloni took a piece of burning charcoal and collected the gas evolved in a test tube.
(a) How will she find the nature of the gas?
(b) Write down the word equations of all the reactions taking place in this process.
(a) She can find the nature of the gas by using a wet litmus paper. After bringing the litmus paper in contact with the gas, if it turns the blue litmus paper into red, it is acidic. Similarly, if it turn the red litmus into blue, it is basic.
(b) (i) Carbon + Oxygen → Carbon dioxide
(ii) Carbon dioxide + Lime water → Milky

Materials: Metals and Non-Metals Class 8 Science NCERT Intext Activities Solved

Activity 1

Take a small iron nail, a coal piece, a piece of thick aluminium wire and a pencil lead. Beat the iron nail with a hammer (Fig. 4.1).

(But take care that you don’t hurt yourself in the process). Try to hit hard. Hit hard the aluminium wire also. Then repeat the same kind of treatment on the coal piece and pencil lead. Record your observations in Table 4.1.
Table 4.1 Malleability of Materials

Object/Material	Change in Shape (Flattens/Breaks into Pieces)
Iron nail	Flattens
Coal piece	Breaks into pieces
Aluminium wire	Flattens
Pencil lead	Breaks into pieces

Solution: This activity shows that iron and aluminium are malleable while coal piece and pencil lead are brittle. Thus, metals are malleable and non-metals are non-malleable.

Activity 2

Recall how to make an electric circuit to test whether electricity can pass through an object or not (Fig. 4.2).

You might have performed the activity with various objects in Class VI. Now, repeat the activity with the materials mentioned in Table 4.2. Observe and group these materials into good conductors and poor conductors.

S. No.	Materials	Good Conductor/Poor Conductor
1.	Iron rod/nail	Good conductor
2.	Sulphur	Poor conductor
3.	Coal piece	Poor conductor
4.	Copper wire	Good conductor

Solution:
It shows that metals are good conductors of electricity and non-metals are poor conductors of electricity.

Activity 3

Let us check the nature of rust formed as a result of the reaction between iron, oxygen and water. Collect a spoonful of rust and dissolve it in a very little amount of water. You will find that the rust remains suspended in water. Shake the suspension well. Test the solution with red and blue litmus papers (Fig. 4.3).

What do you observe? Is the solution acidic or basic?
Solution:
We observed that the red litmus paper turns blue which shows that the nqjure of rust is basic. Blue litmus paper do not show any colour change with the solution.

Activity 4

(To be demonstrated by the teacher in the class)
Take a small amount of powdered sulphur in a deflagrating spoon and heat it. If deflagrating spoon is not available, you may take a metallic cap of any bottle and wrap a metallic wire around it and give it the shape shown in Fig. 4.4 (a).

As soon as sulphur starts burning, introduce the spoon into a gas jar/glass tumbler [Fig. 4.4(a)]. Cover the tumbler with a lid to ensure that the gas produced does not escape. Remove the spoon after some time. Add a small quantity of water into the tumbler and quickly replace the lid. Shake the tumbler well. Check the solution with red and blue litmus papers [Fig. 4.4. (b)].

Solution:
We observed that the solution of oxide turns the blue litmus red which shows that the solution is acidic in nature. This also shows that oxide of non-metals is acidic in nature.

Activity 5

Take a 250 mL beaker/glass tumbler. Fill half of it with water. Now carefully cut a small piece of sodium metal. Dry it using filter paper and wrap it in a small piece of cotton. Put the sodium piece wrapped in cotton into the beaker. Observe carefully.
When reaction stops, touch the beaker. What do you feel? Has the beaker become hot? Test the solution with red and blue litmus papers. Is the solution acidic or basic?

Solution:
On touching the beaker, it was felt hot. The solution turns the red litmus paper to blue which shows it is basic in nature. Blue litmus paper do not show any colour change with the solution.

Activity 6
Take samples of metals and non-metals given in Table 4.3 in separate test tubes and label them as A, B, C, D, E and F. With the help of a dropper add 5 mL of dilute hydrochloric acid to each test tube one by one. Observe the reactions carefully. If no reaction occurs in the cold solution, warm the test tube gently. Bring a burning matchstick near the mouth of each test tube.
Repeat the same activity using dilute sulphuric acid instead of dilute hydrochloric acid. Record your observations in Table 4.3.

Solution:
This activity shows that metals usually displace hydrogen from dilute acids whereas non-metals do not do so and no hydrogen gas is evolved.

Activity 7

Prepare a fresh solution of sodium hydroxide in a test tube by dissolving 3-4 pellets of it in 5 mL of water. Drop a piece of aluminium foil into it. Bring a burning matchstick near the mouth of the test tube. Observe carefully.
Solution:
We observed that a colourless gas is evolved which burns with a pop sound. This shows that aluminium react with bases on heating to produce hydrogen gas.

Activity 8
Take five 100 mL beakers and label them A, B, C, D and E. Take about 50 mL of water in each beaker. Dissolve in each beaker a teaspoonful of each substance as indicated in Fig. 4.6 (a), (i) Keep the beakers undisturbed for some time, (ii) Record you observations in your notebook.

Beaker A: Copper sulphate (CuSO4) + Zinc granule (Zn), Beaker B: Copper sulphate (CuSO4) + Iron nail (Fe)
Beaker C: Zinc sulphate (ZnSO4) + Copper turnings (Cu), Beaker D: Iron sulphate (FeSO4) + Copper turnings (Cu)
Beaker E: Zinc sulphate (ZnSO4) + Iron nail (Fe)
Solution:
In beaker ‘A’ zinc (Zn) replaces copper (Cu) from copper sulphate (CuS04) solution. That is why the blue colour of copper sulphate changes to colourless and a powdery red mass of copper is deposited at the bottom of the beaker. The reaction can be represented as follows:

In beaker B, iron replaces copper from its solution. That is why the blue colour of copper sulphate changes to green colour of ferrous sulphate.

In beaker C, D and E no change in colour or heat evolution is observed. This indicates that the metals are unable to displace the other metals from its solution.

NCERT Solutions for Class 8 Science Chapter 4 – 1 Mark Questions and Answers

Question 1.
Non-metals cannot be drawn into wires. Why ? [DAV2008]
Answer:
Non-metals are not ductile, therefore they cannot be drawn into wires.

Question 2.
Complete the following equation :
Zn + 2HCl ——-> __+ __   [MSE (Chandigarh) 2007]
Answer:
Zn + 2HCl ——-> ZnCl₂ + H₂

Question 3.
Which of the following can be beaten into thin sheets ? [NCERT]

• Zinc
• Phosphorus
• Sulphur
• Oxygen.

Answer:
Zinc.

Question 4.
The number of metals is much ………….. than non-metals.
Answer:
More.

Question 5.
……… are the good conductors of heat and electricity.
Answer:
Metals.

Question 6.
Examples of metals are ………., ……. and ………
Answer:
Iron, sodium and nickel.

Question 7.
Examples of non-metals are ………. , …….. and …….
Answer:
Sulphur, chlorine and oxygen.

Question 8.
Explain the term ‘metallurgy’.
Answer:
Metallurgy is the science of extracting metals from their ores and purifying them for various uses.

Question 9.
State general steps involved in metallurgy of a metal.
Answer:
The general steps of metallurgy are :

• Concentration of ore.
• Reduction of the metal compound.
• Refining of metal.

Question 10.
Metals are (softer/harder) than non-metals.
Answer:
Harder.

Question 11.
Most non-metals are (bad/good) conductors of heat.
Answer:
Bad.

Question 12.
The property that allows the metals to be hammered into thin sheets is called (ductility/ malleability).
Answer:
Malleability.

Question 13.
Melting point of most non-metals is (higher/lower) than metals.
Answer:
Lower.

Question 14.
(Metals/non-metals) display lustre.
Answer:
Metals.

Question 15.
Arrange the following metals in the order of their decreasing chemical activity : magnesium, potassium, iron, gold.
Answer:
Potassium, magnesium, iron, gold.

NCERT Solutions for Class 8 Science Chapter 4 – 2 Mark Questions and Answers

Question 1.
White phosphorous has to be kept in water. Why ? [NCT2007]
Answer:
Phosphorus is to be kept in water to prevent its contact with air because it is highly reactive.

Question 2.
Can you store lemon pickle in an aluminium utensils ? Explain. [NCERT]
Answer:
We cannot store acidic food stuffs in aluminium utensils because aluminium reacts with acids. The food gets spoilt.

Question 3.
One day Reeta went to a jeweller’s shop with her mother. Her mother gave an old gold jewellery to the goldsmith to polish. Next day when they brought the jewellery back, they found that there was a slight loss in its weight. Can you suggest a reason for the loss in weight ? [NCERT]
Answer:
The goldsmith must have used acid to clean the gold jewellery and some gold must have dissolved in it. Therefore, there was loss in weight of the jewellery.

Question 4.
Write short notes on

1. Metallurgical processes
2. Uses of common metals and non-metals
3. Noble metals

Answer:

1. Metallurgical process can be divided into following steps :
   • Concentration of the ore
   • Reduction of metal compound to get free metal
   • Refining of metal.
2. Uses of common metals and non-metals :
   Uses of metals – for making machinery, automobiles, industrial gadgets, building, bridges, cooking utensils, electrical gadgets, jewellery, sheets.
   Uses of non-metals – oxygen is used by plants and animals for their survival, nitrogen is used by plants for their growth, chlorine is used in water purification to kill germs, sulphur is used for making sulphuric acid, tincture iodine has antiseptic properties.
3. Noble metals – Gold, silver and platinum are noble metals. They occur free in nature . and maintain their lustre for a long time. Platinum, gold and silver are used for making jewellery as they do not tarnish.

Question 5.
Purity of gold is 15 carat. What is the percentage’of gold in the ornaments ?
Answer:
24 carat purity of gold =100
∴ 1 carat purity or gold = 100/24
15 carat purity of gold = (100*15)/24 = 62.5 %

Question 6.
Give two uses of sulphur in chemical industry.
Answer:

• It is used in the manufacture of sulphuric acid.
• It is used in the manufacture of carbon disulphide, which is used as an industrial solvent.

Question 7.
How is sulphur useful in agriculture ? How is sulphur useful in medicine ?
Answer:
Sulphur powder is an excellent insecticide and fungicide. It is used in spraying fruit trees.

• Sulphur is the main constituent of skin ointments.
• Metallic sulphides of sulphur are used in the preparation of Ayurvedic medicines.

Question 8.
Give two important uses of silver.
Answer:

• It is used for making coins.
• Silver salts (silver bromide and silver iodide) are used for making photographic films.

Question 9.
Give two uses of gold.
Answer:

• Gold is used for making ornaments.
• Gold foils are used in the preparation of Ayurvedic medicines.

Question 10.
Give two uses of platinum.
Answer:

• It is used as a catalyst in the manufacture of sulphuric and nitric acid.
• Platinum catalytic converters use platinum as catalytic agent.

Question 11.
Which of the following will form acidic oxide and why :
P, K, Na, Ca?
Answer:
P (Phosphorus) will form acidic oxide because it is a non-metal.

Question 12.
You are given two materials X and Y. On hammering X is flattened, but Y breaks. Which one is a metal ?
Answer:
X is a metal because it flattens, i.e., it is malleable.

Question 13.
There are four materials A, B, C and D. A and D are hard and shiny, but B and C are dull and not very hard. Identify the metals and non-metals from A, B, C and D.
Answer:
A and D are metals.
B and C are non-metals.

Question 14.
Gaurav knows that wires can be made from copper and aluminium. He tries to make wire . from sulphur and carbon. Will he succeed ? Give reason also.
Answer:
No, he will not succeed because sulphur and carbon are non-metals. Non-metals are not ductile, that is, they cannot be drawn into wires.

NCERT Solutions for Class 8 Science Chapter 4 – 3 Mark Questions and Answers

Question 1.
What happens when [KVS 2008]
(a) Hydrochloric acid is poured on aluminium foils ?
(b) Sodium is placed in water ?
(c) Sulphur dioxide is dissolved in water ?
(Write the chemical equation of the reaction involved)
Answer:

Question 2.

1. A copper spoon had fallen into a container containing dil.HCl. What would happen to it in three days time ? [DAV2008]
2. Give reasons for the following :
   • Metals are used for making bells.
   • We can’t use pure gold to make jewellery.
3. A metal ribbon bums in air with bright white light and forms a white powder.
   • Which metal is this ?
   • Give the equation of the reaction taking place.
   • The metallic oxide formed would be acidic or basic in nature ?

Answer:

1. Nothing will happen as copper does not react with hydrochloric acid.
   • Metals have the property of sonorosity so they are used for making bells.
   • Pure gold cannot be used for making jewellery because it is very soft.
   • Magnesium.
   • 2Mg + O₂ ——> 2MgO
   • Basic in nature.

Question 3.
Give reasons for the following : [KVS 2007]

1. Silver is used in making mirrors.
2. Aluminium is used to make electrical wire.
3. Iron is used in construction of bridges and houses.
4. Graphite is used as an electrode in the dry cell.
5. Iron sheets are galvanised before use.

Answer:

1. Silver has the ability to reflect light, therefore, it is used for making mirrors.
2. Aluminium is a good conductor of electricity, so, it is used for making electrical wires.
3. Iron is a strong metal, therefore, it is mixed with concrete to make bridges and houses.
4. Graphite is a good conductor of electricity, therefore, it is used as an electrode in dry cell.
5. Iron sheets are galvanised before use so that they do not corrode.

Question 4.
Which of the following statements is correct ? [NCERT]

• All metals are ductile.
• All non-metals are ductile.
• Generally, metals are ductile.
• Some non-metals are ductile.

Answer:
Generally, metals are ductile.

Question 5.
Fill in the blanks : [NCERT]

1. Phosphoms is a very ………… non-metal.
2. Metals are …….. conductors of heat and ………
3. Iron is ……… reactive than copper.
4. Metals react with acids to produce ………. gas.

Answer:

1. reactive
2. good, electricity
3. more
4. hydrogen.

Question 6.
Mark ‘T’ if the statement is true and ‘F’ if it is false. [NCERT]

1. Generally, non-metals react with acids. ( )
2. Sodium is a very reactive metal. ( )
3. Copper displaces zinc from zinc sulphate solution. ( )
4. Coal can be drawn into wires. ( )

Answer:

1. F
2. T
3. F
4. F

Question 7.
Some properties are listed in the following Table. Distinguish between metals and non-metals on the basis of these properties. [NCERT]

Properties	Metals	Non-metals
1. Appearance 2. Hardness 3. Malleability 4. Ductility 5. Heat conduction 6. Conduction of electricity

Answer:

Properties	Metals	Non-metals
1. Appearance	Solid at room temperature except mercury.	They are either solids or gases except bromine (liquid).
2. Hardness	They are hard	They are brittle.
3. Malleability	Malleable	Non-malleable
4. Ductility	Ductile	Non-ductile
5. Heat conduction	Good conductors	Bad conductors
6. Conduction of electricity	Good conductors	Bad conductors

Question 8.
Give reasons for the following : [NCT 2010]

1. Aluminium foils are used to wrap food items.
2. Immersion rods for heating liquids are made up of metallic substances.
3. Copper cannot displace zinc from its salt solution.
4. Sodium and potassium are stored in kerosene.

Answer:

1. Aluminium is a highly malleable metal and can be made into foils. So, it can be used to wrap food items.
2. Metals are good conductors of electricity, therefore, they are used for making immersion rods.
3. Copper is less reactive than zinc. Therefore, it cannot displace zinc from its salt solution.
4. Sodium and potassium are highly reactive metals. On exposure to air, they get oxidized. To avoid this they are stored in kerosene.

Question 9.
Match the substances given in Column I with their uses given in Column II. [NCERT]

Column I	Column II
(a) Gold	(i) Thermometers
(b) Iron	(ii) Electric wire
(c) Aluminium	(iii) Wrapping food
(d) Carbon	(iv) Jewellery
(e) Copper	(v) Machinery
(f) Mercury	(vi) Fuel

Answer:

Column I	Column II
(a) Gold (b) Iron (c) Aluminium (d) Carbon (e) Copper (f) Mercury	(iv) Jewellery (v) Machinery (iii) Wrapping food (vi) Fuel (ii) Electric wire (i) Thermometers

 Question 10.
What happens when [NCERT]

1. Dilute sulphuric acid is poured on copper plate ?
2. Iron nails are placed in copper sulphate solution ? Write word equations of the reactions involved.

Answer:

1. When sulphuric acid is poured on copper plate, copper sulphate and hydrogen gas are produced.
   Copper + Sulphuric acid ——-> Copper sulphate + Hydrogen (gas).
2. When iron nails are placed in copper sulphate solution, iron sulphate and copper are formed.
   Iron + Copper sulphate ——-> Iron sulphate + Copper

Question 11.
Saloni took a piece of burning charcoal and collected the gas evolved in a test tube. [NCERT]
(a) How will she find the nature of the gas ?
(b) Write down word equations of all the reactions taking place in this process.
Answer:
(a) The nature of gas can be found by passing it lime water, which will turn milky.

Question 12.
List different uses of metals that you come across in everyday life.
Answer:
Metals are used for making

• machinery
• automobiles, aeroplanes, trains, etc.
• pins, cooking utensils, electrical gadgets.
• electrical wires.
• thin sheets used for wrapping of food items, medicines, etc.

Question 13.
Choose appropriate words from the brackets and complete the statements.

1. Noble gases are found in (free state/compound forms).
2. Non-metals are generally (malleable/brittle).
3. Potassium after combustion will form (acidic oxide/basic oxide).
4. (Iodine/bromine) has antiseptic properties.
5. German silver has (copper/silver) as major constituent.

Answer:

1. Free state
2. Brittle
3. Basic oxide
4. Iodine
5. Copper

Question 14.
State whether the following statements are True or False :

1. Sodium is more reactive than magnesium.
2. Magnesium reacts with cold water.
3. All metals exist in solid form at room temperature.
4. Gallium has a low melting point.
5. Gold is alloyed with copper to make it hard.

Answer:

1. False
2. True
3. True
4. False
5. True

Question 15.
From among the set of metals — sodium, zinc, iron, copper, silver, select the following giving equations for each reaction :
(a) Two metals which will liberate hydrogen from water.
(b) One metal which is used to prepare hydrogen gas in the laboratory.
(c) One metal which will displace copper from copper sulphate solution.
(d) One metal which will not displace copper from copper sulphate solution.
Answer:

NCERT Solutions for Class 8 Science Chapter 4 MCQs

Question 1.
Which of the following properties is generally not shown by metals?
(a) Ductility
(b) Sonorous
(c) Dullness
(d) Electrical conduction
Answer:
(c)

Question 2.
The most abundant element in the universe is
(a) hydrogen
(b) oxygen
(c) helium
(d) carbon
Answer:
(a)

Question 3.
The ability of metals to be drawn into wires is known as
(a) ductility
(b) conductivity
(c) malleability
(d) sonorousity
Answer:
(a)

Question 4.
The most abundant element in the earth crust is
(a) iron
(b) oxygen
(c) silicon
(d) aluminium
Answer:
(b)

Question 5.
Galvanisation is a method qf protecting iron from rusting by coating with a thin layer of
(a) silver
(b) galium
(c) zinc
(d) aluminium
Answer:
(c)

Question 6.
The most abundant ihetal in earth crust is
(a) Cu
(b) Al
(c) Fe
(d) Zn
Answer:
(b)

Question 7.
An alloy is
(a) a compound
(b) a heterogeneous mixture
(c) a homogeneous mixture
(d) an element
Answer:
(c)

Question 8.
In extraction of copper, the flux used is
(a) FeO
(b) Si02
(c) CaO
(d) FeSi03
Answer:
(b)

Question 9.
Alloys are homogeneous mixtures of a metal with a metal or non-metal. Which among the following aljoys contain non-metal as one of its constituents?
(a) Amalgam
(b) Brass
(c) Bronze
(d) Steel
Answer:
(d)

Question 10.
Which of the following is purest form of carbon?
(a) Diamond
(b) Graph’ite
(c) Fullerenes
(d) Charcoal
Answer:
(c)

Question 11.
Which among the following alloys contain mercury as one of its constituents?
(a) Alnico
(b) Solder
(c) Stainless steel
(d) Zinc Amalgam
Answer:
(d)

Question 12.
Which of the following methods is suitable for preventing an iron frying pan from rusting?
(a) Applying paint
(b) Applying grease
(c) Applying a coating of zinc
(d) all of these
Answer:
(c)

Question 13.
Generally, non-metals are not conductors of electricity, which of the following is a good conductor of electricity?
(a) Fullerenes
(b) Graphite
(c) Diamond
(d) Sulphur
Answer:
(b)

Question 14.
Food cans are coated with tin and not with zinc because
(a) zinc is costlier than tin
(b) zinc is less reactive than tin
(c) zinc is more reactive than tin
(d) zinc has a higher melting point than tin
Answer:
(a)

Question 15.
Electrical wires have a coating of an insulating materials. The material, generally used is
(a) sulphur
(b) graphite
(c) PVC
(d) none of these
Answer:
(c)

Synthetic Fibres and Plastics Class 8 Science NCERT Textbook Questions

Question 1.
Explain why some fibres are called synthetic.
Answer:
Some fibres are called synthetic fibres because they are made by man using chemicals.

Question 2.
Mark (✓) the correct answer.
Rayon is different from synthetic fibres because
(a) it has a silk-like appearance.
(b) it is obtained from wood pulp.
(c) its fibres can also be woven like those of natural fibres.
Answer:
(b) it is obtained from wood pulp.

Question 3.
Fill in the blanks with appropriate words.
(a) Synthetic fibres are also called ____ or ____ fibres.
(b) Synthetic fibres are synthesised from a raw material called _____
(c) Like synthetic fibres, plastic is also a _____
Answer:
(a) man-made, artificial fibres
(b) petrochemicals
(c) polymer

Question 4.
Give examples which indicate that nylon fibres are very strong.
Answer:
The following examples indicate that nylon fibres are very strong.
(i) They are used for making parachutes and ropes for rock climbing.
(ii) They are used in making seat-belts, fishing nets, tyre cord, a string for sports rackets and musical instruments.

Question 5.
Explain why plastic containers are favoured for storing food.
Answer:
Plastic containers are favoured for storing food because of the following reasons:
(i) the plastics do not react with the food stored in them.
(ii) the plastics are lightweight and are strong.
(iii) they are easy to handle and safe.

Question 6.
Explain the difference between thermoplastic and thermosetting plastics.
Answer:

Thermoplastics	Thermosetting plastics
(i) These plastics softened on heating and can be bent easily.	(i) These plastics when moulded once, can’t be softened again.
(ii) They do not lose their plasticity.	(ii) They lose their plasticity.
(iii) Examples are polyethene, PVC, etc.	(iii) Examples are bakelite and melamine.

Question 7.
Explain why the following are made of thermosetting plastics.
(a) Saucepan handles
(b) Electric plugs/switches/plugboards
Answer:
(a) Since, thermosetting plastics are a bad conductor of heat and do not get heated up while cooking, they are used for making saucepan handles.
(b) Since thermosetting plastics are a bad conductor of electricity and the electric current does not pass through such plastics, they are used for making electric plugs/switches/plugboards.

Question 8.
Categorise the materials of the following products into ‘can be recycled’ and ‘can not be recycled’.
Telephone instruments, plastic toys, cooker handles, carry bags, ballpoint pens, plastic bowls, plastic covering on electrical wires, plastic chairs, electrical switches.
Answer:

Can be recycled	Cannot be recycled
Plastic toys carry bags, plastic bowls, plastic covering on electrical wires, plastic chairs.	Telephone instruments, cooker handles, ballpoint pens, electrical switches.

Question 9.
Rana wants to buy shirts for summer. Should he buy cotton shirts or shirts made from synthetic material? Advise Rana, giving your reason.
Answer:
He should buy cotton shirts. This is because cotton has more capacity to hold moisture than synthetic clothes. In summers we have extensive sweating which is easily soaked by cotton shirts and hence, cotton clothes are much better than the clothes made from synthetic material.

Question 10.
Give examples to show that plastics are non-corrosive in nature.
Answer:
The literal meaning of non-corrosive is resistant to get destroyed by chemical action.
Following are the examples that show that plastics are non-corrosive in nature.

• Plastic containers do not react with items stored in it.
• They do not get rusted when exposed to moisture and air.
• They do not decompose when left in open for a long period.

Synthetic Fibres and Plastics Class 8 Science NCERT Intext Activities Solved

Activity 1
Take an iron stand with a clamp. Take a cotton thread of about 60 cm length. Tie it to the clamp so that it hangs freely from it as shown in Fig. 3.3.

At the free end suspend a pan so that weight can be placed in it. Add weight one by one till the thread breaks. Note down the total weight required to break the thread. This weight indicates the strength of the fibre. Repeat the same activity with threads of wool, polyester, silk and nylon. Tabulate the data as shown in Table 3.1. Arrange the threads in order of their increasing strength.
Observation Table 3.1

S. No.	Type of Thread/ Fibre	Total Weight required to break the thread
1.	Cotton	12 gm
2.	Wool	70 gm
3.	Silk	50 gm
4.	Nylon	100 gm

(Precaution: Note that all threads should be of the same length and most of the same thickness.)

Activity 2
Take two cloth pieces of the same size, roughly half a metre square each. One of these should be from natural fibre. The other could be a synthetic fibre. You can take the help of your parents in selecting these pieces. Soak the pieces in different mugs each containing the same amount of water. Take the pieces out of the containers after five minutes and spread them in the sun for a few minutes. Compare the volume of the water remaining in each container.
Solution:
It is observed that the volume of water of the container in which natural fibre is soaked contains less water as compared to the container in which synthetic fibre is soaked. Thus, natural fibre absorbs more water as compared to synthetic fibre. When both the fibres were spread in the sun, it was observed that synthetic fibre took less time to dry than natural fibre.

NCERT Solutions for Class 8 Science Chapter 3 – 1 Mark Questions and Answers

Question 1.
Explain why some fibres are called synthetic. [NCERT]
Answer:
Some fibres are called synthetic because they are made by human beings.

Question 2.
Mark the correct answer.
Rayon is different from synthetic fibres because [NCERT]

• It has a silk-like appearance.
• It is obtained from wood pulp.
• Its fibres can also be woven like those of natural fibres.

Answer:

• It is obtained from wood pulp.

Question 3.
Give examples which indicate that nylon fibres are very strong.
Answer:
Parachutes and nylon ropes are used for rock climbing.

Question 4.
Name the plastic whose sheets are used for packing liquids.
Answer:
Polythene.

Question 5.
Why is teflon used as tape for sealing purpose ?
Answer:
Becausee of its toughness, teflon is used as tape for sealing purpose.

Question 6.
Name the first fully synthetic fibre.
Answer:
Nylon.

Question 7.
Why nylon is used for making parachutes ?
Answer:
Nylon is used for making parachutes, because it is very strong, elastic and light.

Question 8.
Name the material used for making ropes for rock climbing.
Answer:
Nylon.

Question 9.
What is polyester ?
Answer:
Polyester is made up of the repeating units of an ester.

Question 10.
Name the plastic used for making polythene bags.
Answer:
Polythene bag is made of plastic which is a polymer of ethene.

Question 11.
What name is given to plastics which can be re-set a number of times ?
Answer:
Thermoplastics.

Question 12.
Classify the following into thermosetting and thermoplastics-combs, bakelite, melamine, toys.
Answer:
Thermosetting – bakelite, melamine
Thermoplastics – combs, toys

Question 13.
Why are the chemicals in the laboratory stored in plastic containers ?
Answer:
Plastics are non-reactive, so they can be used for storing chemicals.

Question 14.
Can you store pickles in plastic containers ? Why ?
Answer:
Plastics are non-reactive, so pickles can be stored in them.

Question 15.
Why are the electric wires covered with plastic ?
Answer:
Plastic is a poor conductor of electricity, therefore, the wires are covered with it.

Question 16.
Why do we use plastic cookwares in microwave ovens ?
Answer:
We use plastic cookware in microwave ovens, because they are not affected by heat but the food is cooked.

Question 17.
Tin takes about 100 years to degenerate. Is it biodegradable or non-biodegradable ?
Answer:
Tin is non-biodegradable.

Question 18.
Is it advisable to use recycled plastic containers for storing food ?
Answer:
No, we should not use recycled plastic containers for storing food because they contain colouring agents.

Question 19.
As a responsible citizen, what are the 4R’s we should remember ?
Answer:
Reduce, Reuse, Recycle and Recover

NCERT Solutions for Class 8 Science Chapter 3 – 2 Mark Questions and Answers

Question 1.
Aperson has to make a non-stick pan. He has three types of plastic-Bakelite, Teflon and PVC. Which plastic will he use for coating and why ?
Answer:
The person will use Teflon because it is not affected by heat and does not react chemically with other substances.

Question 2.
Explain the difference between thermoplastic and thermosetting plastics. [NCERT]
Answer:

Thermosetting	Thermoplastic
(i) These plastics can be moulded and (ii) e.g.,Bakelite and melamine.	(i) These plastics can be moulded and reset a number of times. (ii) e.g. Polythene and PVC.

 Question 3.
Differentiate between natural and synthetic fibres.
Answer:
Natural fibres are obtained from nature, e.g., cotton whereas synthetic fibres are made by man, e.g., nylon.

Question 4.
How is rayon made ? Give one advantage of using rayon.
Answer:
Rayon is obtained from wood pulp by treating it chemically. It is cheaper than silk, but can be woven like silk fibre.

Question 5.
Is nylon fibre so strong, that we can use it to make parachutes ?
Answer:
Yes, nylon is very strong and it can be used for making parachutes.

Question 6.
Give some uses of PET.
Answer:
PET is used for making bottles, utensils, fibres and wires.

Question 7.
Give the composition of Polycot and Polywool.
Answer:
Polycot is a mixture of polyester and cotton, Poly wool is a mixture of polyester and wool.

Question 8.
What properties of plastics make it useful for many things ?
Answer:
Plastics can be recycled, reused, coloured, melted, rolled into sheets or made into wires, so they are very useful.

Question 9.
Why is melamine used for making kitchenware ?
Answer:
Melamine resists fire and can tolerate heat better than other plastics. So, it is used for making kitchenware.

Question 10.
Buckets made up of plastics are better. Why ?
Answer:
Buckets made up of plastic are better because they are light, strong and durable.

NCERT Solutions for Class 8 Science Chapter 3 – 3 Mark Questions and Answers

Question 1.
Give three advantages of polythene over natural materials. [MSE (Chandigarh)]
Answer:
Three advantages of polythene over natural materials are :

• It is strong but flexible.
• Can be rolled into sheets.
• Water resistant.

Question 2.
Give one use each of bakelite, nylon and acrylic.
Answer:
Bakelite is used for making plugs and switches. Nylon is used in textile industry to produce clothes. Acrylic is used as a substitute of natural wool for knitting sweaters, blankets etc.

Question 3.
Fill in the blanks with appropriate words. [NCERT]

1. Synthetic fibres are also called ……….. or ……….
2. Synthetic fibres are synthesised from raw material called …………
3. Like synthetic fibres, plastic is also a …………..

Answer:

1. artificial, man-made
2. mono or petrochemicals
3. polymers.

Question 4.
Explain why plastic containers are favoured for storing food. [NCERT]
Answer:
Food can be stored in plastic containers because

• Plastics are non-reactive.
• Plastics are light and strong.
• Plastics are durable.

Question 5.
Explain why the following are made of thermosetting plastics : [NCERT]

1. Saucepan handles
2. Electric plugs/switches/plug boards.

Answer:

1. Saucepan handles are made of thermosetting plastics because they are bad conductors of heat.
2. Electric plugs/switches/plug boards are made of thermosetting plastics because they are bad conductors of electricity.

Question 6.
Rana wants to buy shirts for summer. Should he buy cotton shirts or shirts made from synthetic material ? Advice Rana, giving your reason.
Answer:
Rana should buy cotton shirts. Cotton clothes are preferred in summer because they absorb sweat and the person feels cool whereas synthetic materials do not absorb sweat and the person feels uncomfortable.

Question 7.
Give examples to show that plastics are noncorrosive in nature. [NCERT]
Answer:

• Buckets made of iron get rusted but those made of plastic are not rusted.
• Food can be stored in plastic containers, as they are resistant to chemicals in the food
• Teflon coated pans are used instead of metallic as it doesnot react with chemicals in the food.

Question 8.
Give three advantages of rayon.
Answer:
Advantages of rayon are :

• It is cheap.
• It can be dyed in many colours.
• It can be woven like silk.

Question 9.
What are the advantages of nylon ?
Answer:
Nylon fibre is strong, elastic and light. It is lustrous and easy to wash.

Question 10.
Give some uses of nylon.
Answer:
Nylon can be used for making socks, ropes, tents, toothbrushes, sleeping bags, curtains, parachutes and ropes for rock climbing

NCERT Solutions for Class 8 Science Chapter 3 – 5 Mark Questions and Answers

Question 1.
Categorise the materials of the following products into ‘can be recycled’ and ‘cannot be recycled’. [NCERT]
Telephone instruments, plastic toys, cooker handles, carry bags, ball point pens, plastic bowls, plastic covering on electrical wires, plastic chairs, electrical switches.
Answer:

Can be recycled	Non-biodegradable Materials
Toys, carry bags, plastic bowls, plastic covering on electrical wires, plastic chairs.	Telephone instruments, cooker handles, electric switches, ball point pens, electrical switches.

 Question 2.
Match the terms of Column A correctly with the phrases given in Column B. [NCERT]

Column A	Column B
(a) Polyester (b) Teflon (c) Rayon (d) Nylon	(i) Prepared by using wood pulp. (ii)Used for making parachutes and stockings. (iii) Used to make non-stick cookwares. (v) Fabrics do not wrinkle easily.

Answer:

Column A	Column B
(a) Polyester	(iv) Fabrics do not wrinkle easily.
(b) Teflon	(iii) Used to make non-stick cookwares.
(c) Rayon	(i) Prepared by using wood pulp.
(d) Nylon	(ii) Used for making parachutes and stockings.

 Question 3.
‘Manufacturing synthetic fibres is actually helping conservation of forests’. Comment. [NCERT]
Answer:
The said statement is correct to a certain extent. The forests would be conserved if synthetic fibres are used, but other effects of synthetic fibres are more harmful. Disposal of synthetic fibres causes lot of environmental pollution. When synthetic fibres bum, lot of smoke is produced.

Question 4.
‘Avoid plastics as far as possible’. Comment on this advice. [NCERT]
Answer:
Plastics are very useful, but it causes serious environmental and health concern :

• Plastics are non-biodegradable.
• Careless disposal of plastic bags, chokes, drains and blocks the soil.
• If eaten by cows, it can kill them.
• Plastic bags can also contaminate foodstuffs due to poisonous dyes getting absorbed into food

Question 5.
How is plastic useful in healthcare industry ?
Answer:
In healthcare, plastics are used

• for packaging of tablets
• as threads for stitching wounds
• in syringes
• doctor gloves
• for making a number of medical instruments.

Question 6.
“Even though plastics are very useful, they are not environment friendly.” Justify the statement.
Answer:
Plastics are very useful, but their disposal is a big problem. Plastics are non-biodegradable and take many years to decompose. They release a lot of poisonous fumes, when burnt so they cause environmental pollution.

Question 7.
Give methods by which pollution due to plastics can be solved.
Answer:
Pollution due to plastics can be solved by following methods :

• Avoid the use of plastics as far as possible.
• Use bags, made of jute or cloth.
• Biodegradable and non-biodegradable wastes should be separated and disposed off separately.
• Plastics should be recycled and reused.

NCERT Solutions for Class 8 Science Chapter 3 MCQs

Question 1.
Electrical switches are made of
(a) nylon
(b) bakelite
(c) polythene
(d) melamine
Answer:
(b)

Question 2.
Out of the following, which is not biodegradable ?
(a) Vegetable peels
(b) Plastic bags
(c) Cotton
(d) Jute
Answer:
(b)

Question 3.
Clothes made of which fabric are best suited for hot climate ?
(a) Cotton
(b) Nylon
(c) Acrylic
(d) Polycot
Answer:
(a)

Question 4.
Out of the following, which is not a natural fibre ?
(a) Cotton
(b) Silk
(c) Jute
(d) Rayon
Answer:
(d)

Question 5.
Naturally occurring po/ymer is
(a) cellulose
(b) polyester
(c) nylon
(d) PVC
Answer:
(a)

Question 6.
Plastic used for coating non-stick pans is
(a) PVC
(b) ester
(c) bakelite
(d) melamine
Answer:
(d)

Question 7.
Pickles are kept in plastic containers because plastic containers are
(a) non-corrosive
(b) light
(c) colourful
(d) cheap
Answer:
(a)

Question 8.
Which of the following is a thermoplastic
(a) Bakelite
(b) Melamine
(c) Polythene
(d) Jute
Answer:
(c)

Question 9.
Which of the following can be recycled?
(a) Plastic bowls
(b) Ballpoint pens
(c) Telephone instruments
(d) Electrical switches
Answer:
(a)

Question 10.
Which material is best suited for covering electric wires?
(a) Plastic bowls
(b) PVC
(c) Polystyrene
(d) Nylon
Answer:
(b)

Microorganisms: Friend and Foe Class 8 Science NCERT Textbook Questions

Question 1.
Fill in the blanks.
(a) Microorganisms can be seen with the help of a _____
(b) Blue-green algae fix ______ directly from the air to enhance the fertility of soil.
(c) Alcohol is produced with the help of _____
(d) Cholera is caused by ______
Answer:
(a) microscope
(b) nitrogen
(c) yeast
(d) bacteria

Question 2.
Tick the correct answer.
(a) Yeast is used in the production of
(i) sugar
(ii) alcohol
(iii) hydrochloric acid
(iv) oxygen
Answer:
(ii) alcohol

(b) The following is an antibiotic:
(i) sodium bicarbonate
(ii) streptomycin
(iii) alcohol
(iv) yeast
Answer:
(ii) streptomycin

(c) Carrier of malaria-causing protozoan is:
(i) female Anopheles mosquito
(ii) cockroach
(iii) housefly
(iv) butterfly
Answer:
(i) female Anopheles mosquito

(d) The most common carrier of communicable diseases is
(i) ant
(ii) housefly
(iii) dragonfly
(iv) spider
Answer:
(ii) housefly

(e) The bread or idli dough rises because of:
(i) heat
(ii) grinding
(iii) growth of yeast cells
(iv) kneading
Answer:
(iii) growth of yeast cells

(f) The process of conversion of sugar into alcohol is called
(i) nitrogen fixation
(ii) moulding
(iii) fermentation
(iv) infection
Answer:
(iii) fermentation

Question 3.
Match the organisms in column A with their action in column B.

A	B
(i) Bacteria	(a) Fixing nitrogen
(ii) Rhizobium	(b) Setting of curd
(iii) Lactobacillus	(c) Baking of bread
(iv) Yeast	(d) Causing malaria
(v) A protozoan	(e) Causing cholera
(vi) A virus	(f) Causing AIDS
	(g) Producing antibodies

Answer:
(i) (e)
(ii) (a)
(iii) (b)
(iv) (c)
(v) (d)
(vi) (f)

Question 4.
Can microorganisms be seen with the naked eye? If not, how can they be seen?
Answer:
The microorganisms cannot be seen with our naked eyes because they are very small in size. Some of these, such as fungus growing on bread, can be seen with a magnifying glass. Others cannot be seen without the help of a microscope.

Question 5.
What are the major groups of microorganisms?
Answer:
Microorganisms are classified on the basis of their size into four major groups. These groups are:
(a) Bacteria
(b) Fungi
(c) Protozoa
(d) Some algae

Question 6.
Name the microorganisms which can fix atmospheric nitrogen in the soil.
Answer:
Rhizobium, Clostridium and Azotobacter.

Question 7.
Write 10 lines on the usefulness of microorganisms in our lives.
Answer:
Microorganisms are useful to us in many ways. For example,

• Bacteria like Lactobacillus convert milk into curd.
• Bacteria are also involved in the making of cheese.
• Acetobacter aceti is used for producing acetic acid from alcohol.
• Yeast is used in the commercial production of alcohol, wine and bakery products.
• Some specific microorganisms are helpful in manufacturing of antibiotics.
• Microorganisms act as cleansing agents and decompose the waste products into manure.
• Dead or weakened microbes are used in the preparation of vaccines.
• Some bacteria fix atmospheric nitrogen and increase soil fertility.
• Algae, yeast, fungi or bacteria may be used as an ingredient or a substitute for protein-rich foods that are suitable for human or animal consumption.
• Some microorganisms are taken as probiotics, that are believed to provide health benefits when consumed.

Question 8.
Write a short paragraph on the harms caused by microorganisms.
Answer:
Microorganisms are harmful to us in many ways. For example, microorganisms, called pathogens cause disease in humans, plants and animals. Pathogens or germs enter a healthy body through air, water, contaminated food and infected person by direct or indirect contact or by the carrier. Common ailments like cold, influenza (flu), cough, polio, chicken pox are caused by viruses. Foot and mouth diseases in the cattle are also caused by viruses. Typhoid, tuberculosis (TB) are caused by bacteria. Anthrax a dangerous human and cattle diseases is also caused by bacteria.

Diseases like dysentery and malaria are caused by protozoa. Ringworm is caused by fungi. Several microbes causes diseases in plants and thus reduces the yield. Citrus canker, a bacterial disease, affects trees of citrus fruit and is spread by air. Bhendi yellow vein mosaic disease is caused by a virus and is spread by insects in lady fingers. Rust of wheat is a fungal disease spread through air. Microorganisms that grow on our food sometimes produce toxic substances. These make the food poisonous causing serious illness and even death. This food-borne illness is called food poisoning.

Question 9.
What are antibiotics? What precautions must be taken while taking antibiotics?
Answer:
Antibiotics are the medicines which kill or stop the growth of the disease-causing microbes. They are manufactured by growing specific microorganisms. They are used to cure a variety of diseases.

It is important to take antibiotic only on the advice of a qualified doctor. One must finish the course prescribed by the doctor to make the drug more effective. Antibiotics must not be taken unnecessarily because it may kill beneficial bacteria also. Antibiotics are, however, not effective against cold and flu as they are caused by viruses.

Microorganisms: Friend and Foe Class 8 Science NCERT Intext Activities Solved

Activity 1
Collect some moist soil from the field in a beaker and add water to it. After the soil particles have settled down, observe a drop of water from the beaker under a microscope. What do you see?
Solution:
It is observed that some tiny organisms are moving around.

Activity 2
Take a few drops of water from a pond. Spread on a glass slide and observe through a microscope.
Solution:
It is observed that some tiny organisms are moving around.

Activity 3
Jake 1/2 kg flour (atta or maida), add some sugar and mix with warm water. Add a small amount of yeast powder and knead to make a soft dough. What do you observe after two hours? Did you find the dough rising?

Solution:
It is observed that the dough begins to rise up in volume. Yeast reproduces rapidly and releases C02 during respiration. Etubble of this gas fill the dough and increase its volume.

Activity 4

Take 500 ml. beaker filled upto 3/4 with water. Dissolve 2-3 teaspoons of sugars in it. Add half a spoon of yeast powder to the sugar solution. Keep it covered in a warm place for 4-5 hours. Now smell the solution. Can you get a smell?
Solution:
It is observed that the solution smell like alcohol. This process of conversion of sugar in alcohol is known as fermentation.

Activity 5

Take two pots and fill each pot half with soil. Mark them A and B. Put plant waste in pot A and things like polythene bags, empty glass bottles and broken plastic toys in pot B. Put the pots aside. Observe them after 3-4 weeks.
Solution:
It is observed that plant waste in pot A has been decomposed, whereas the polythene bags, empty glass bottles and broken plastic toys in pot B did not undergo such changes.

NCERT Solutions for Class 8 Science Chapter 2 – 1 Mark Questions and Answers

Question 1.
Name the bacteria responsible for the disease typhoid. [MSE (Chandigarh) 2008]
Answer:
Salmonella typhi.

Question 2.
Chicken pox is caused by ………. virus. [KVS 2008]
Answer:
Varicella zoster.

Question 3.
………….. (disease) is caused by mycoplasma. [KVS 2008]
Answer:
Pleuropneumonia.

Question 4.
Name the toxin released by T.B. bacteria.[MSE (Chandigarh) 2007]
Answer:
Tuberculin toxin is released by T.B. bacteria.

Question 5.
Which microorganism is the cause of malaria ? [NCT 2006]
Answer:
A Protozoan, Plasmodium.

Question 6.
Write two diseases caused by bacteria. [NCT2005]
Answer:
Two diseases caused by bacteria are tuberculosis and diphtheria.

Question 7.
Name any two items that are prepared by using yeast. [KVS 2005]
Answer:
Yeast is used to prepare bread and alcohol.

Question 8.
Fill in the blanks : [NCERT]

1. Microorganisms can be seen with the help of a …………..
2. Blue-green algae fix ………… directly from air to enhance fertility of soil.
3. Alcohol is produced with the help of ………….
4. Cholera is caused by ……………

Answer:

1. Microscope
2. Nitrogen
3. Yeast
4. Bacteria.

Question 9.
Tick the correct answer : [NCERT]

• (a) Yeast is used in the production of
  (i) sugar
  (ii) alcohol
  (iii) hydrochloric acid
  (iv) oxygen.
• (b) The following is an antibiotic
  (i) Sodium bicarbonate
  (ii) Streptomycin
  (iii) Alcohol
  (iv) Yeast.
• (c) Carrier of malaria-causing protozoan is
  (i) female anopheles mosquito
  (ii) cockroach
  (iii) housefly
  (iv) Butterfly.
• (d) The most common carrier of communicable diseases is
  (i) ant
  (ii) housefly
  (iii) dragonfly
  (iv) spider.
• (e) The bread or idli dough rises because of
  (i) heat
  (ii) grinding
  (iii) growth of yeast cells
  (iv) kneading.
• (f) The process of conversion of sugar into alcohol is called
  (i) nitrogen fixation
  (ii) moulding
  (iii) fermentation
  (iv) infection.

Answer:
(a) —> (ii)
(b) —> (ii)
(c) —> (i)
(d) —> (ii)
(e) —> (iii)
(f) —> (iii)

Question 10.
Match the organisms in Column I with their action in Column II. [NCT2010, NCERT]

Column I	Column II
(a) Bacteria (b) Rhizobium (c) Lactobacillus (d) Yeast (e) A protozoan (f) A virus	(i) Fixing nitrogen (ii) Setting of curd (iii) Baking of bread (iv) Causing malaria (v) Causing cholera (vi) Causing AIDS

Answer:

Column I	Column II
(a) Bacteria (b) Rhizobium (c) Lactobacillus (d) Yeast (e) A protozoan (f) A virus	(i) Causing cholera (ii) Fixing nitrogen (iii) Setting of curd (iv) Baking of bread (v) Causing malaria (vi) Causing AIDS

Question 11.
Name the microorganisms which can fix atmospheric nitrogen in the soil. [NCERT]
Answer:
Rhizobium, Clostridium md Azotobacter fix atmospheric nitrogen.

Question 12.
Can microorganisms be seen with the naked eye ? If not, how can they be seen ? [NCERT]
Answer:
No, microorganisms cannot be seen with the naked eye. They can only be seen with the help of microscope.

Question 13.
What are the major groups of microorganisms ? [NCERT]
Answer:

• Bacteria
• Fungi
• Protozoa
• Algae.

Question 14.
What are microorganisms ?
Answer:
Microorganisms are organisms that are so small that they can only be seen through a microscope.

Question 15.
Name two diseases caused by viruses.
Answer:
Influenza and cough.

NCERT Solutions for Class 8 Science Chapter 2 – 2 Mark Questions and Answers

Question 1.
Describe the role of blue-green algae in fertility of soil. [KVS 2006, MSE (Chandigarh) 2008]
Answer:
Blue-green, algae, also called cyanobacteria, can fix atmospheric nitrogen into usable , compounds. These are then used as fertilizers.

Question 2.
Name three habitats of microorganisms. [MSE (Chandigarh) 2008, 2006]
Answer:
Microorganisms are present in soil, water, outer space and inside the body of animals.

Question 3.
Name the bacterium found in the roots of pea plant. How is this bacterium useful for human beings ? [NCT2007]
Answer:
Rhizobium is the bacterium found in the roots of pea plant. The. bacterium absorbs the atmospheric nitrogen and converts it to nitrates.

Question 4.
What is a vaccine ? Why is it important to vaccinate small children ? [DAV2006]
Answer:
Vaccine is prepared from weak or dead disease-causing microbe. Vaccine is given to healthy persons to prevent occurrence of disease. It is important to vaccinate small children because it creates antibodies in blood.

Question 5.

1. Give full form of ORS.
2. What is vaccination ? [DAV2007]

Answer:

1. ORS — Oral Rehydration Solution.
2. Vaccination is a method to immunise the body against diseases by making the body’s immune system produce antibodies against the disease-causing microbe in the vaccine.

Question 6.
Mention two important uses of fungi. [KVS 2006]
Answer:
Uses of fungi:

• They convert dead organic matter into simple soluble minerals and gases, which can be used again by plants.
• Fungi like yeast is used in bread, beer and wine.

Question 7.
How is pasteurised milk obtained ? [NCT 2010]
Answer:
In pasteurisation, the milk is heated to 62.5°C for 30 minutes or to 71.5°C for 15 seconds. It is then rapidly cooled to 10°C and packed in airtight containers.

Question 8.
Draw a neat and well-labelled diagram of Spirogyra.
Answer:

Question 9.
Draw a labelled diagram of Rhizopus.
Answer:

Question 10.
Draw a labelled diagram of Chlamydomonas. [DAV 1997]
Answer:

Question 11.
Draw a labelled diagram of Amoeba.
Answer:

Question 12.
How are viruses different from other microorganisms ?
Answer:
Viruses reproduce only inside the host organisms that is, bacterial, plant or animal cell.

Question 13.
Give two examples where microorganisms are useful at home.
Answer:
At home microorganisms are used for preparation of curd and cakes.

Question 14.
How are microorganisms useful commercially ?
Answer:
Microorganisms are used for the large scale production of alcohol, wine and acetic acid (vinegar).

Question 15.
How do microorganisms clean the environment ?
Answer:
Microorganisms degrade the harmful substances and clean the environment.

Question 16.
How can we prevent a person from getting Hepatitis B ?
Answer:

• By giving boiled water for drinking.
• By vaccination.

Question 17.
Name one disease caused by bacteria and one disease caused by virus in cattle.
Answer:

• Bacteria – Anthrax.
• Virus – Foot and mouth disease.

NCERT Solutions for Class 8 Science Chapter 2 – 3 Mark Questions and Answers

Question 1.

• Tuberculosis is a highly infectious disease. Justify the statement.
• Which vitamin helps in the prevention of common cold ? [MSE (Chandigarh) 2008]

Answer:

• Tuberculosis is a highly infectious disease. TB is transmitted through minute droplets of infected sputum on phelgm, by drinking milk of an infected animal.
• Common cold is prevented by taking vitamin C.

Question 2.
Draw a labelled diagram of virus. [KVS 2008, DAV 2006]
Answer:

Question 3.
Can you store pickles in iron containers ? Why ? [KVS 2007]
Answer:
We can not store pickles in iron containers because the acid present in the pickles reacts with iron. This can cause food poisoning, if consumed.

Question 4.
What precautions must be taken while taking antibiotics ?
Answer:
Antibiotics should be taken after consulting a doctor. The complete dose of the antibiotics should be taken as prescribed. They should not be taken unnecessarly because they will kill the useful bacteria.

Question 5.

1. Write the causal organism of cholera.
2. Write any two symptoms of this disease.
3. Why ORS should be given to the patients suffering from cholera ? [MSE (iChandigarh) 2007]

Answer:

1. Cholera is caused by Vibrio cholerae.
2. Two symptoms of cholera are :
   • profuse and painless watery diarrhoea.
   • muscular cramps.
3. ORS should be given to the patients suffering from cholera to avoid excessive loss of body fluids.

Question 6.
Why are viruses considered to be on the borderline between living organisms and non-living things ? [DAV2007]
Answer:
Viruses cannot reproduce, respond to changes or use energy to grow. Since viruses reproduce in the host cell, scientist regard viruses as a link between living and non-living.

Question 7.
How are bacteria beneficial for us ? [NCT 2006]
Answer:
Bacteria are useful to us as :

• Nitrogen fixing bacteria increase the fertility of the soil.
• They can be used to form curd, alcohol, etc.
• They can decompose organic matter.

Question 8.
Write three types of bacteria on the basis of their shape. Give one example of each. [MSE (Chandigarh) 2005]
Answer:
Three types of bacteria are :

1. Bacillus or rod-shaped, e.g., Lactobacillus.
2. Coccus or spherical, e.g., Streptococcus.
3. Spirillum or spiral, e.g., Vibrio.

Question 9.
(a) Are bacteria plants or animals ? Give reasons in support of your answer.
(b) Write two differences between autotrophic and heterotrophic bacteria. [DAV2005]
Answer:
(a) Bacteria is considered as plant due to the presence of a rigid cell wall in it.
(b)

Autotrophic bacteria	Heterotrophic bacteria
(i) Chlorophyll is present. (ii) Synthesize their own food.	(i) Chlorophyll is absent. (ii) Depend on readymade food from other sources.

Question 10.
How does a housefly transmit diseases ? [MSE (Chandigarh) 1999]
Answer:
A housefly gets attracted towards garbage and excreta. The harmful microorganisms present in excreta and garbage easily stick to its fine array of body hair and are thus, transferred to food stuffs whenever they sit on them and a result food gets poisoned.

Question 11.

1. What are antibiotics ?
2. How are antibiotics manufactured ?
3. Name two important antibiotics.

Answer:

1. Medicines which kill or stop the growth of the disease causing microorganisms are called antibiotics.
2. The antibiotics are manufactured by growing specific microorganisms.
3. Two important antibiotics are Tetracycline and Bacitracin.

Question 12.
What will happen if you take antibiotics when not needed ?
Answer:
If you take antibiotics when not needed, you help bacteria in your body to develop resistance to them. Next time when you fall ill and need these antibiotics, they would be less effective.

Question 13.
How does a vaccine act ?
Answer:
The vaccine acts by making the body’s immune system to produce antibodies against the disease-causing microbe in the vaccine. The antibodies attack and destroy the weakened microbe as it enters the body.

Question 14.
How is common cold spread ?
Answer:
When a person suffering from common cold sneezes, fine droplets of moisture carrying thousands of viruses causing common cold are spread in the air. The viruses may enter the body of a healthy person while breathing.

Question 15.
How can you prevent the spread of communicable diseases ?
Answer:
It is better to avoid contact with the infected person. We should keep distance from infected persons.

NCERT Solutions for Class 8 Science Chapter 2 – 5 Mark Questions and Answers

Question 1.
Describe the nitrogen cycle with the help of a neat and labelled diagram. [MSE (Chandigarh) 2005, 2007]
Answer:

Question 2.
Write 10 lines on the usefulness of microorganisms in our lives. [NCERT]
Answer:
Microorganisms are useful in our lives in the following ways :

• Bacteria cause the decay of dead plants and animals.
• Nitrogen fixing bacteria convert the atmospheric nitrogen into nitrates.
• Bacteria are used in the production of vinegar, curd, cheese, etc.
• Bacteria are used in sewage disposal plants.
• Scientists have discovered ways to change bacteria so that they produce valuable medical, agricultural and industrial products.

Question 3.
Write a short paragraph on the harms caused by microorganisms. [NCERT]
Answer:

• Microorganisms cause diseases in human beings, plants and animals.
• Microorganisms spoil food and cause food poisoning.

Question 4.
How can we control the spread of malaria or dengue ?
Answer:
All mosquitoes breed in water. Hence, by keeping the surroundings clean and dry, we can prevent mosquitoes from breeding. We should not allow water to collect in coolers, flower pots, etc. We should wear full sleeves shirts in the evenings and at night. We can also use mosquito repellant creams and mosquito nets.

NCERT Solutions for Class 8 Science Chapter 2 MCQs

Question 1.
Microorganisms exhibiting the characteristics of living and non-living organisms are known as
(a) bacteria
(b) virus
(c) algae
(d) fungi
Answer:
(b)

Question 2.
A person bitten by dog gets
(a) malaria
(b) tetanus
(c) typhoid
(d) rabies
Answer:
(d)

Question 3.
Amoebic dysentery is transmitted by
(a) sneezing
(b) using contaminated water
(c) direct contact
(d) wound
Answer:
(b)

Question 4.
Anthrax in cattle is caused by
(a) fungi
(b) virus
(c) bacteria
(d) algae
Answer:
(c)

Question 5.
Smut of rice is caused by
(a) virus
(b) protozoa
(c) fungi
(d) bacteria
Answer:
(c)

Question 6.
Wheat, maize and oats are preserved by
(a) using sugar and salt
(b) pasteurisation
(c) drying
(d) using chemical preservatives
Answer:
(c)

Question 7.
Jams and jellies are preserved by
(a) drying
(b) using chemical preservatives
(c) using acetic acid
(d) using heat and cold treatments
Answer:
(b)

Question 8.
Pasteurisation is the method used for preserving
(a) milk
(b) jams
(c) pickles
(d) grains
Answer:
(a)

Question 9.
Fermentation is the process used for making
(a) curd
(b) cheese
(c) idlis
(d) chappatis
Answer:
(c)

Crop Production and Management Class 8 Science NCERT Textbook Questions

Question 1.
Select the correct word from the following list and fill in the blanks.
float, water, crop, nutrients, preparation
(a) The same kind of plants grown and cultivated on a large scale at a place is called _____
(b) The first step before growing crops is _______ of the soil.
(c) Damaged seeds would ______ on top of the water.
(d) For growing a crop, sufficient sunlight and ______ and ______ from the soil are essential.
Answer:
(a) crop
(b) preparation
(c) float
(d) water, nutrients

Question 2.
Match items in column A with those in column B.

A	B
(i) Kharif crops	(a) Food for cattle
(ii) Rabi crops	(b) Urea and superphosphate
(iii) Chemical fertilisers	(c) Animal excreta, cow dung, urine and plant waste
(iv) Organic manure	(d) Wheat, gram, pea
	(e) Paddy and maize

Answer:
(i) (e)
(ii) (d)
(iii) (b)
(iv) (c)

Question 3.
Give two examples of each.
(a) Kharif crop
(b) Rabi crop
Answer:
(a) Kharif crop: Paddy and maize
(b) Rabi crop: Wheat and gram

Question 4.
Write a paragraph in your own words on each of the following.
(a) Preparation of soil
(b) Sowing
(c) Weeding
(d) Threshing
Answer:
(a) Preparation of soil: Soil preparation is necessary before growing a crop. It involves tilling and loosening the soil. This allows the roots to penetrate deep in the soil and to breath easily even when they are deep.

(b) Sowing: The process of putting seeds into the soil is called sowing. The tool used traditionally for sowing seeds is funnel-shaped. Nowadays a seed drill is used for sowing with the help of tractors. This tool sows the seed uniformly at a proper distance and depth.

(c) Weeding: Some undesirable plants grow along with crop and these unwanted plants are called weeds. The process of removing these unwanted plants is called weeding.

(d) Threshing: The process of separating the grain seeds from the chaff is called threshing.

Question 5.
Explain how fertilisers are different from manure.
Answer:

Fertilisers	Manures
(i) A fertiliser is an inorganic salt.	(i) Manure is a natural substance obtained by the decomposition of cattle dung, human waste and plant residues.
(ii) A fertiliser is prepared in factories.	(ii) Manure can be prepared in the fields.
(iii) A fertiliser does not provide any humus to the soil.	(iii) Manure provides a lot of humus to the soil.
(iv) Fertilisers are very rich in plant nutrients like nitrogen, phosphorus and potassium.	(iv) Manure is relatively less rich in plant nutrients.

Question 6.
What is irrigation? Describe two methods of irrigation which conserve water.
Answer:
The artificial method of watering the plants for assisting in their growth is called irrigation. Main sources of irrigation are wells, tube-wells, ponds, lakes, rivers.
Two methods which help us to conserve water are:
(i) Sprinkler irrigation system: This irrigation system has an arrangement of vertical pipes with rotating nozzles on the top. It is more useful in the uneven and sandy land where sufficient water is not available.

(ii) Drip irrigation system: This irrigation system has an arrangement of pipes or tubes with very small holes in them to water plants drop by drop just at the base of the root. It is very efficient as water is not wasted at all.

Question 7.
If wheat is sown in the kharif season, what would happen? Discuss.
Answer:
Wheat crop is sown from November/December to March/April. It is grown in winter and requires less water. If wheat is sown in Kharif season, its production will be decreased considerably.

Question 8.
Explain how soil gets affected by the continuous plantation of crops in a field.
Answer:
Continuous plantation of crops makes the soil poorer in certain nutrients as the crops take up nutrients from the soil. The soil becomes infertile. It does not get enough time to replenish the nutrients.

Question 9.
What are the weeds? How can we control them?
Answer:
The undesirable and unwanted plants which grow naturally along with the crop are called weeds. The growth of weeds can be controlled by adopting many ways. Tilling before sowing of crops helps in the uprooting and killing of weeds, which may then dry up and get mixed with the soil. Weeds are also controlled by using certain chemicals, called weedicides. Weedicides are sprayed in the fields to kill the weeds.

Question 10.
Arrange the following boxes in the proper order to make a flow chart of sugarcane crop production.

Answer:

Question 11.
Complete the following word puzzle with the help of clues given below.
Down
1. Providing water to the crops.
2. Keeping crop grains for a long time under proper conditions.
5. Certain plants of the same kind grown on a large scale.
Across
3. A machine used for cutting the matured crop.
4. A rabi crop that is also one of the pulses.
6. A process of separating the grain from the chaff.
Answer:

Crop Production and Management Class 8 Science NCERT Intext Activities Solved

Activity 1

Take a beaker and fill half of it with water. Put a handful of wheat seeds and stir well. Wait for some time.
Solution:
We observe that most of the seeds sink while some float on water. Damaged seeds become hollow and lighter so they float. In this way, we can separate damage seeds from the healthier ones.

Activity 2

Jake moong or gram seeds and germinate them. Select three equal sized seedlings out of these. Now take three empty glasses or similar vessels. Mark them A, B and C.To glass A add little amount of soil mixed with a little cow dung manure. In glass B put the same amount of soil mixed with a little urea. Take the same amount of soil in glass C without adding anything [Fig. 1.2(a)]. Now pour the same amount of water in each glass and plant the seedlings in them. Keep them in a safe place and water them daily. After 7 to 10 days observe their growth [Fig. 1.2(b)].

Solution:
After 7-10 days we observed that the growth was fastest in glass B followed by glass A. Glass C showed mini-mum growth.

Activity 3
Make the following Table in your notebook and complete it.

S. No.	Food	Sources
1.	Milk	Cow, Buffalo, She-goat, She-camel
2.	Meat	Goat, Hen, Pig, Duck, Sheep
3.	Egg	Hen, Duck, Goose
4.	Honey	Honey bee

NCERT Solutions for Class 8 Science Chapter 1 – 1 Mark Questions and Answers

Question 1.
Select the correct word from the following list and fill in the blanks : [NCERT]
float, water, crop, nutrients, preparation
(a) The same kind of plants grown on a large scale at a place is called …………..
(b) The first step before growing crops is …………. of the soil.
(c) Damaged seeds would …………. on top of water.
(d) For growing a crop sufficient sunlight, …………….. and …….. the soil are essential.
Solution:
(a) crop
(b) preparation
(c) float
(d) nutrients, water

Question 2.
Match items in column ‘A’ with those in column ‘B’ [NCERT]

(A)	(B)
1. Kharif crops 2. Rabi crops 3.Chemicalfertilisers 4. Organic manure	(a) Food for cattle (b) Urea and super phosphate (c) Animal excreta,cowdung, urine and plant waste. (d) Wheat, gram, pea. (e) Paddy and maize

Solution:

(A)	(B)
1. Kharif crops 2. Rabi crops 3. Chemical fertilisers 4. Organic manure	(e) Paddy and maize (d) Wheat, gram, pea (b) Urea and super phosphate (c) Animal excreta, cow dung, urine and plant waste.

Question 3.
What are crops?
Solution:
Crops are plants of the same kind grown in large quantities for food.

Question 4.
What is the basis of classification of crops in our country?
Solution:
In our country, crops are classified on the basis of the season in which they grow.

Question 5.
What are kharif crops?
Solution:
The crops which are sown in the rainy season and harvested in September/October are called kharif crops.

Question 6.
What are summer crops?
Solution:
The crops which are grown in the summer season and harvested before rainy season are called summer crops or zayed crops.

Question 7.
Name two summer season crops.
Solution:
Moong and muskmelon are summer season crops.

Question 8.
What are rabi crops?
Solution:
The crops which are grown in the winter season and harvested in March/April are called rabi crops.

Question 9.
Why paddy cannot be grown in the summer season?
Solution:
Paddy requires a lot of water, so it can only be grown during rainy season.

Question 10.
What is meant by agricultural practices?
Solution:
The activities undertaken by farmers over a period of time for cultivation of crops are known as agricultural practices.

Question 11.
Write a paragraph in your own words on preparation of soil.
Solution:
Soil is prepared by tilling i.e., loosening and turning of soil.

Question 12.
Name the tool used for tilling of soil.
Solution:
A plough is used for tilling of soil.

Question 13.
What are crumbs?
Solution:
A ploughed field may have big pieces of soil called crumbs.

Question 14.
How are crumbs broken?
Solution:
The crumbs are broken with the help of a plank.

Question 15.
Why should loose soil be levelled?
Solution:
Loose soil be levelled for sowing and irrigation.

Question 16.
How is levelling of soil done?
Solution:
Levelling of soil is done with the help of a leveller.

Question 17.
How is ploughing done these days?
Solution:
Now a days ploughing is done by tractor having a multipronged plough.

Question 18.
What is meant by sowing?
Solution:
Sowing is the process of putting seeds in the soil.

Question 19.
What is meant by good quality seeds?
Solution:
The good quality seeds means clean and healthy seeds of a good variety free from diseases.

Question 20.
What is the advantage of sowing seeds with a seed drill?
Solution:
The advantage of sowing seeds with a seed drill is that the seeds are sown at a proper depth under the soil and the distance between them is uniform.

Question 21.
What are manure and fertilisers?
Solution:
The substances which are added to the soil in the form of nutrients for the healthy growth of plants are called manure and fertilisers.

Question 22.
What is organic manure?
Solution:
Manure obtained from animal or plant waste such as cattle dung, droppings is called organic manure.

Question 23.
What is meant by crop rotation?
Solution:
Growing crops alternatively to prevent depletion of any one nutrient from soil is called crop rotation.

Question 24.
What is meant by irrigation?
Solution:
The supply of water to crops in the fields at different intervals is called irrigation.

Question 25.
What is the drip system of irrigation?
Solution:
Falling of water drop by drop at the roots of the plant is called drip irrigation.

Question 26.
Why should weeds be removed?
Solution:
Weeds compete with the crop plants for water, nutrients, space and light and thus affect the growth of the crop. So, they should be removed.

Question 27.
Name the process of removal of weeds.
Solution:
Weeding is the process of removal of weeds.

Question 28.
How is harvesting done in our country?
Solution:
Harvesting in our country is done either manually by sickle or by a machine called harvester.

Question 29.
Name the farm machine used for harvesting and threshing both.
Solution:
Combine.

Question 30.
What is meant by winnowing?
Solution:
After threshing, the grain is separated from the chaff, with the help of wind. This is known as winnowing.

Question 31.
How are food grains stored?
Solution:
Food grains are dried in the sun to remove the excess moisture and then stored.

Question 32.
Why should grains be dried before storage?
Solution:
Grains should be dried before storage to remove the excess moisture in them, so that microbes are not able to attack the grains.

Question 33.
What is meant by animal husbandry?
Solution:
The study of the care of animals is known as animal husbandry.

Question 34.
Name some animals from whom milk can be obtained.
Solution:
Milk can be obtained from cow, buffalo, she goat and she camel.

Question 35.
How is fish useful for us?
Solution:
Fish is highly nutritious and easily digestible food. Cod liver oil from fish is also a rich source of vitamin D.

Question 36.
Name some animals which are reared for their meat.
Solution:
Sheep, goat, pigs, chicken and fish are reared for their meat.

Question 37.
Why is honey so useful?
Solution:
Honey is an antiseptic and its enzymes help in digestion. It is also used for making several ayurvedic medicines.

NCERT Solutions for Class 8 Science Chapter 1 – 2 Mark Questions and Answers

Question 1.
If wheat is sown in the kharif season, what would happen? Discuss. [NCERT]
Solution:
The farmer will not get a good crop because wheat should be sown in winter season.

Question 2.
Explain how soil gets affected by the continuous plantation of crops in a field. [NCERT]
Solution:
When the crops are planted continuously in a field, the soil becomes deficient in nutrients.

Question 3.
What are weeds? How can we control them? [NCERT]
Solution:
Weeds are unwanted plants in the fields. It can be controlled by

• During tilling they are removed.
• By removing them manually.
• By using weedicides.

Question 4.

(a) Give two examples of each : [NCT 2011, NCERT]
(i) Kharif crop
(ii) Rahi crop
(b) Can you explain why most crops have a particular season in which they grow?
Solution:
(a) (i) Groundnut and cotton.
(ii) Pea and mustard.
(b) Most crops have a particular season in which they grow because different crops need different temperature, humidity and rainfall.

Question 5.
What is a seed drill?
Solution:
A seed drill is used for sowing seeds. It has a funnel shaped opening leading to long tubes attached to a plough. Seeds are put into the funnel. As the plough makes furrows in the soil, the seeds are deposited in the soil by the drill.

Question 6.
Give two reasons why seeds should be sown at correct distance.
Solution:
Seeds should be sown at a correct distance. The reasons are:

• If the seeds are too close, they will not get enough water, sunlight and nutrients.
• If the seeds are too far apart, there is wastage of field space.

Question 7.
Give two methods by which threshing can be done.
Solution:
Threshing can be done manually by making oxen or buffaloes trample over the cut crop or by a machine called thresher.

Question 8.
A farmer grow moong during the rainy season. Will he get a good crop?
Solution:
The farmer will not get a good crop of moong because moong should be grown during summer season.

Question 9.
Why does loosening of soil allow roots to breathe easily?
Solution:
When soil is loosened, the roots can breathe easily because there is more air present in the soil.

Question 10.
A farmer never leaves his field fallow. Will he get a good crop?
Solution:
If the field is never left fallow, the soil will become deficient in certain nutrients and the farmer will not get a good crop.

NCERT Solutions for Class 8 Science Chapter 1 – 3 Mark Questions and Answers

Question 1.
Define lodging. How does it happen? [MSE (Chandigarh) 2008, 2006]
Solution:
Lodging is the falling of crop plants at the grain maturation stage. It happens due to untimely rains and strong winds.

Question 2.

1. What is harvesting?
2. Mention two important uses of tilling the soil. [MSE (Chandigarh) 2008]

Solution:

1. Cutting and gathering of crops after maturation is known as harvesting.
2. Uses of tilling the soil are :
   • It improves air circulation.
   • Roots can penetrate deeper into the soil.

Question 3.

1. Define crop.
2. Name two categories of crops based on season. [KVS 2005]
3. What are pesticides? [KVS 2005]

Solution:

1. The plants of same kind grown at a place is referred to as crop.
2. Two categories of crop based on season are kharif and rabi crops.
3. Pesticides are chemicals used to protect crops from harmful organisms called pests.

Question 4.

• Earthworms are nature’s ploughmen. How?
• How is soil a resource for all living organisms? Give any two points. [DAV2006]

Solution:

• They make burrows in soil and bring lower fertile layer above the ground.
  • It is habitat for many living organisms.
  • Plants grow in soil which provide food, shelter, material for clothes.
  • Plants grows in soil and provide O2.
  • Decomposition occurs in soil.

Question 5.
What is irrigation? Describe two methods of irrigation which conserve water. [NCERT]
Solution:
Supply of water to crops at appropriate intervals is called Irrigation.
Two methods of irrigation are :

• Sprinkler system – Where water is sprinkled on the crops as if it is raining.
• Drip system – In this system, the water falls drop by drop just at the position of the roots.

Question 6.
Name three natural methods of replenishing the nutrients of the soil. Are these natural methods sufficient to maintain the fertility of the soil?
Solution:
Field fallow, crop rotation and mixed cropping are three natural methods of replenishing the nutrients of the soil. These natural methods are not enough and farmers have to resort to manures and fertilisers.

Question 7.
Give three reasons, why soil should be turned and loosened?
Solution:

• It allows the roots to penetrate deep in the soil.
• It helps the growth of earthworms and microbes in the soil.
• Various nutrients held in the dead organisms are released back in the soil.

Question 8.
What are the three steps involved in the preparation of soil?
Solution:

• Ploughing the soil to loosen it.
• Levelling the soil to ensure uniform distribution of water and nutrients.
• Manuring to provide nutrients to the soil.

Question 9.
Name the three tools used for ploughing and give the function of each.
Solution:

• Plough – It is used for tilling of soil, adding fertilisers to the crop, removing the weeds, scrapingof soil.
• Hoe – It is used for removing weeds and for loosening the soil.
• Cultivator – Used for ploughing.

Question 10.
How is organic manure obtained?
Solution:
Farmers dump plant and animal waste in pits at open places and allow it to be decomposed by microorganisms. This decomposed material is converted into organic manure.

NCERT Solutions for Class 8 Science Chapter 1 – 5 Mark Questions and Answers

Question 1.

1. What are the two ways of sowing the seeds? [DAV2007]
2. Give any three advantages of ploughing.

Solution:

1. Seeds can be sown manually or by seed drills.
2. Ploughing has following advantages :
   • Loose soil has lot of air trapped which allows roots to breathe.
   • Loose soil allows the roots to penetrate deeper.
   • Loose soil helps the growth of microbes and other organisms.

Question 2.

1. What will happen if field is not ploughed before sowing the seeds? Give any two disadvantages. [DAV2006]
2. How are perishable food items stored on a commercial scale?
3. Why should excessive supply of water be avoided?
4. What are weeds?

Solution:

1. Disadvantages:
   • Seeds cannot be sown at proper depth.
   • Water and air holding capacity of soil will be poor.
2. Perishable food items can be stored in deep freezers and cold storages.
3. Roots get damaged and the plants die because of excessive supply of water.
4. They are unwanted plants which grow along with the cultivated plants.

Question 3.
(a) Why does farmer rotate crops in the field?
(b) Differentiate between manure and fertiliser. [DAV2005]
Solution:
(a) To replenish the nutrients of the soil.
(b)

Manure	Fertiliser
(i) It is natural. (ii) It is organic. (iii) It adds humus to the soil. (iv) It is not nutrient specific. (v) It is cheap. (vi) It is  prepared in the fields.	(i) It is man-made. (ii) It is inorganic. (iii) It does not add humus. (iv) It is nutrient specific. (v) It is costly. (vi) It is prepared in factories.

or
(a) (i) While spraying pesticides, nose and mouth should be closed.
(ii) Position of the farmer should be such that the wind blows away from his face.
(iii) Immediately after spraying is done, hands should be washed, face and mouth should be cleaned with water.

Question 4.
Arrange the following boxes in proper order to make a flow chart of sugarcane crop production: [NCERT]

Solution:

Question 5.
List the steps involved in crop production in a flow chart.
Solution:

Question 6.
Explain the method used these days to sow seeds.
Solution:
These days the seed drill is used for sowing seeds with the help of a tractor. This sows the seed uniformly at a proper distance and depth. Seeds get covered by soil during sowing with a drill. This prevents damage caused by birds. Sowing by using seed drill saves time and labour.

Question 7.
What are the advantages of organic manure?
Solution:
The advantages of organic manure are :

• It enhances the water holding capacity of the soil.
• It makes the soil porous due to which exchange of gases takes place.
• The number of friendly microbes is increased.
• The organic manure improves the texture of the soil.

Question 8.
How does a plough work?
Solution:
A plough is an agricultural implement used for tilling and loosening of soil. It has a triangular iron strip called plough share. Plough shaft is the main part made of a long wooden log. The other end is hung on the bull’s necks. The plough can be with two bulls and one person.

Question 9.
Write a paragraph in your own words on each of the following : [NCERT]

1. Preparation of soil
2. Sowing
3. Weeding
4. Threshing

Solution:

1. Preparation of soil : Preparation of the soil involves loosening and turning the soil.
   This process, known as ploughing, is done by using a wooden or iron plough which is pulled either by an animal or by tractors. Loose soil is then levelled by using a wooden or iron leveller.
2. Sowing : Seeds are sown after preparation of the soil. Seeds can be sown manually or by seed drills by the process called broadcasting. Seeds should be sown at the correct depth and at correct distance.
3. Weeding : The process of removing weeds from a field is called weeding. Weeding can be done manually by pulling the weeds out by hand or by using a harrow to uproot them. Weeding can also be done by spraying special chemicals called weedicides.
4. Threshing: Threshing is the process of separating the grain from the cut crop. Threshing can be done manually by making oxen or buffaloes trample over the cut crop or by using a machine called thresher.

NCERT Solutions for Class 8 Science Chapter 1 – Multiple Choice Questions

Question 1.
Paddy can be grown in
(a) summer season
(b) autumn
(c) rainy season
(d) winter
Solution:
(c)

Question 2.
Wheat can be grown in
(a) winter
(b) rainy season
(c) spring
(d) summer
Solution:
(a)

Question 3.
Which of the following is a rabi crop?
(a) Paddy
(b) Maize
(c) Mustard
(d) Soyabean
Solution:
(c)

Question 4.
Loosening and turning of the soil is known as
(a) tilling
(b) broadcasting
(c) transplantation
(d) manuring
Solution:
(a)

Question 5.
Sowing the seeds manually is known as
(a) ploughing
(b) broadcasting
(c) tilling
(d) transplantation
Solution:
(b)

Question 6.
The method of transferring seedlings from nursery to field is known as
(a) broadcasting
(b) transplantation
(c) crop rotation
(d) harvesting
Solution:
(b)

Question 7.
Leaving the agricultural land uncultivated for one or more seasons is known as
(a) field fallow
(b) crop rotation
(c) manuring
(d) threshing
Solution:
(a)

Question 8.
Chemical substances rich in specific nutrients are called
(a) manures
(b) fertilisers
(c) pesticides
(d) weedicides
Solution:
(b)

Question 9.
Chemicals which kill weeds are known as
(a) fertilizers
(b) pesticides
(c) weedicides
(d) none of these
Solution:
(c)

Question 10.
Cutting and gathering of crops after maturation is known as
(a) harvesting
(b) threshing
(c) broadcasting
(d) tilling
Solution:
(a)

Exercise 16.1 | Class 8th Mathematics

1. Find the values of the letters in each of the following and give reasons for the steps involved.
   
   
   Solution:
   

2.

Solution:

3.

Solution:

4.

Solution:

5.

Solution:
3 × B = B
⇒ B = D
3 × A = CA
⇒ 3 × 5 = 15
Thus A = 5 and C = 1
Hence A = 5, B = 0 and C = 1

6.

Solution:
5 × B = B
⇒ B = 0 or 5
5 × A = CA
5 × 5 = 25
Only possible when B = 0
Thus A = 5 and C = 2
Hence A = 5, B = 0 and C = 2

7.

Solution:
B × 6 = B
6 × 4 = 24 → B = 4 and 2 is carried to
6 × A = BB
⇒ 6 × 7 = 42 + 2 (carried on) = 44
Thus B = 7
Hence A = 7 and B = 4

Solution:
1 + B = 0
1 + 9 = 10 → unit digit is 0 and 1 is carried to A
+ 1 +1 (carried on) = B = 9
A + 2 = 9 ⇒ A = 9 – 2 = 7
Hence A = 7 and B = 9

9.

Solution:
B + 1 = 8 ⇒ B = 8 – 1 = 7
A + B = a number with unit digit 1
A + B = 11
⇒ A + 7 = 11
⇒ A = 11 – 7 = 4 (1 Carried to)
Now 1 carried on + 2 + A = B
3 + A = 7
⇒ A = 7 – 3 = 4
Hence A = 4, B = 7

10.

Solution:
9 = A + B
9 = 1 + 8 or 2 + 7 or 3 + 6 or 4 + 5 or 8 + 1 or 7 + 2 or 6 + 3 or 5 + 4 or 0 + 9 or 9 + 0
Now 0 is required at unit place
2 + A = 10
⇒ A = 10 – 2 = 8
B = 9 – 8 = 1
1 + 6 + 1 (carried on) = A = 8
Hence A = 8 and B = 1

Exercise 16.2 | Class 8th Mathematics

1. If 21y5 is a multiple of 9, where y is a digit, what is the value of y?
   Solution:
   A number is divisible by 9 if the sum of its digits is also divisible by 9.
   Sum of the digits of 21y5 = 2 + 1 +y + 5 = 8 + y
   (8 + y) ÷ 9 = 1
   ⇒ 8 + y = 9
   ⇒ y = 9 – 8 = 1
   Hence, the required value of y = 1.

2. If 31z5 is a multiple of 9, where z is a digit, what is the value of z?
Solution:
A number is a multiple of 9 when the sum of its digits is also divisible by 9.
Sum of the digits of 31z5 = 3 + 1 + z + 5
3 + 1 + 2 + 5 = 9k where k is an integer.
For k = 1,
3 + 1 + z + 5 = 9
⇒ z = 9 – 9 = 0
For k = 2,
3 + 1 + z + 5 = 18
⇒ z = 18 – 9 = 9
k = 3 is not possible because 3 + 1 + z + 5 = 27
⇒ z = 27 – 9 = 18 which is not a digit.
Hence the required value of z is 0 or 9

3. If 24x is a multiple of 3, where x is a digit, what is the value of x?
Solution:
Since 24x is a multiple of 3, the sum of digits 6 + x is a multiple of 3; so 6 + x is one of these numbers; 0, 3, 6, 12, 15, 18, ……..
6 + x = 3k where k is any integer.
For k = 0,
6 + x = 3 × 0
⇒ 6 + x = 0
x = -6. Not possible
For k = 1,
6 + x = 3 × 1
⇒ 6 + x = 3
⇒ x = 3 – 6 = -3. Not possible
For k = 2,
6 + x = 3 × 2
⇒ 6 + x = 6
⇒ x = 6 – 6 = 0
2 + 4 + 0 = 6 multiple of 3
For k = 3,
6 + x = 3 × 3
⇒ x = 9 – 6 = 3
2 + 4 + 3 = 9 multiple of 3
For k = 4,
6 + x = 3 × 4
⇒ 6 + x = 12
⇒ x = 12 – 6 = 6
2 + 4 + 6 = 12 which is multiple of 3
For k = 5,
6 + x = 3 × 5
⇒ x = 15 – 6 = 9
2 + 4 + 9 = 15 which is multiple of 3
For k = 6,
6 + x = 3 × 6
⇒ x = 18 – 6 = 12 not possible as x is digit
Hence the required values of x are 0, 3, 6 or 9.

4. If 31z5 is a multiple of 3, where z is a digit, what might be the value of z?
Solution:
A number is a multiple of 3 if the sum of its digits is divisible by 3.
3 + 1 + z + 5 = 3k where k is an integer
⇒ 9 + z = 3k
⇒ z = 3k – 9
Here, k = 0, 1, 2 is not possible as z is a digit of the number.
For k = 3,
z = 3 × 3 – 9 = 9 – 9 = 0
9 + 0 = 9 multiple of 3
For k = 4,
z = 3 × 4 – 9 = 12 – 9 = 3
9 + 3 = 12 multiple of 3
For k = 5,
z = 3 × 5 – 9 = 15 – 9 = 6
9 + 6 = 15 multiple of 3
For k = 6,
z = 3 × 6 – 9 = 18 – 9 = 9
9 + 9 = 18 multiple of 3
For k = 7,
z = 3 × 7 – 9 = 21 – 9 = 12 not possible as z is a digit
Hence, the required values of 2 are 0, 3, 6 and 9.

Extra Questions | Class 8th Mathematics

Exercise 15.1 | Class 8th Mathematics

1. The following graph shows the temperature of a patient in a hospital, recorded every hour.
   
   (a) What was the patient’s temperature at 1 pm?
   (b) When was the patient’s temperature 38.5°C?
   (c) The patient’s temperature was the same two times during the period given. What were the two times?
   (d) What was the temperature at 1:30 pm? How did you arrive at your answer?
   (e) During which periods did the patient’s temperature show an upward trend?
   Solution:
   (a) The patient’s temperature at 1 pm was 36.5°C
   (b) The patient’s temperature was 38.5°C at 12:00 noon.
   (c) The patients temperature was 36.5°C at 1 pm and 2 pm.
   (d) The temperature at 1:30 pm was 36.5°C. We have taken the mid value of 1 pm. and 2 pm, i.e., 1:30 p.m and proceed perpendicularly upwards to meet the horizontal line showing 36.5°C.
   (e) During 9 am to 10 am and 10 am to 11 am, the temperature showed upwards trend.

2. The following line graph shows the yearly sales figures for a manufacturing company.

(a) What were the sales in (i) 2002 (ii) 2006?
(b) What were the sales in (i) 2003 (ii) 2005?
(c) Compute the difference between the sales in 2002 and 2006.
(d) In which year was there the greatest difference between the sales as compared to its previous year?
Solution:
(a) The sales in the year 2002 was ₹ 4 crore and in the year 2006 was ₹ 8 crore.
(b) The sales in the year 2003 was ₹ 7 crore and in 2005 was ₹ 10 crore.
(c) Sales in 2002 = ₹ 4 crore
Sales in 2006 = ₹ 8 crores
Difference = ₹ (8 – 4) crore = ₹ 4 crore.
(d) The greatest difference between the sales was in the year 2005, as compared to previous year.

3. For an experiment in Botany, two different plants, plant A and plant B, were grown under similar laboratory conditions. Their heights were measured at the end of each week for 3 weeks. The results are shown by the following graph.

(a) How high was plant A after (i) 2 weeks (ii) 3 weeks
(b) How high was plant B after (i) 2 weeks (ii) 3 weeks
(c) How much did plant A grow during the 3rd week?
(d) How much did plant B grow from the end of the 2nd week to the end of the 3rd week?
(e) During which week did plant A grow most?
(f) During which week did plant B grow least?
(g) Were the two plants of the same height during any week shown here? Specify.
Solution:
(a) The height of plant A (i) after 2 weeks was 7 cm (ii) after 3 weeks was 9 cm.
(b) The height of plant B (i) after 2 weeks was 7 cm (ii) after 3 weeks was 10 cm.
(c) Plant A grew 7 cm to 9 cm i.e, 2 cm.
(d) Plant B grew 7 cm to 10 cm i.e., 3 cm.
(e) Plant A grew most in a 2nd week i.e., 5 cm.
(f) Plant B grew the least in a first week i.e., 1 cm.
(g) Yes, the two plants grew the same height at the end of 2nd week i.e., 7 cm.

4. The following graph shows the temperature forecast and the actual temperature for each day of a week.

(a) On which days was the forecast temperature the same as the actual temperature?
(b) What was the maximum forecast temperature during the week?
(c) What was the minimum actual temperature during the week?
(d) On which day did the actual temperature differ the most from the forecast temperature?
Solution:
(a) On Tuesday, Friday and Sunday, the forecast temperature was the same as the actual temperature i.e., 20°C, 15°C and 35°C respectively.
(b) The forecast maximum temperature during the week was 35°C
(c) The minimum actual temperature during the week was 17.5°C
(d) On Thursday, the actual temperature differed the most from the forecast temperature
i.e., 22.5°C – 15°C = 7.5°C.

5. Use the tables below to draw linear graphs.
(a) The number of days a hillside city recovered show in different years.

Year	2003	2004	2005	2006
Days	8	10	5	12

(b) Population (in thousands) of men and women in a village is different years.

Year	2003	2004	2005	2006	2007
Number of men	12	12.5	13	13.2	13.5
Number of women	11.3	11.9	13	13.6	12.8

Solution:

6. A courier-person cycle from a town to a neighbouring suburban area to deliver a parcel to the merchant. His distance from the town at different times is shown by the following graph.

(a) What is the scale taken for the time axis?
(b) How much time did the person take for travel?
(c) How far is the place of the merchant from the town?
(d) Did the person stop on his way? Explain?
(e) During which period did he ride fastest?
Solution:
(a) Scale taken on time-axis i.e., the x-axis is 4 units = 1 hour
(b) Total time taken by the person for the total journey is 3 hours 30 minutes.

(c) The place of the merchant is at a distant of 22 km from the town.

7. Can there be a time-temperature graph as follows? Justify your answer.

Solution:
(i) It represents a time-temperature graph where temperature increases as the time increase.
(ii) It shows a time-temperature graph where temperature decreases as the time increases.
(iii) It does not represent a time-temperature graph. Here the temperature is increasing at a constant time which is not possible.
(iv) It represents a time-temperature graph where the temperature remains constant when the time is increasing.

Exercise 15.2 | Class 8th Mathematics

1. Plot the following points on a graph sheet. Verify if they lie on a line.
   (a) A (4, 0), B(4, 2), C(4, 6), D(4, 2.5)
   (b) P(1, 1), Q(2, 2), R(3, 3), S(4, 4)
   (c) K(2, 3), L(6, 3), M(5, 5), N (2, 5)
   Solution:
   
   Yes, all the coordinate points lie on a line.
   
   Yes, all the coordinate points lie on a line.
   
   No, the coordinate points do not lie on a line.

2. Draw the line passing through (2, 3) and (3, 2). Find the coordinates of the points at which this line meets the x-axis and y-axis.

Solution:
CD is the required line passing through the points A(2, 3), B (3, 2) which meets x-axis at C(5, 0) and y-axis at D(0, 5).

3. Write the coordinates of the vertices of each of these adjoining figures.

Solution:
Required coordinates are as follows:
Coordinates of rectangle OABC are:
O(0, 0), A(2, 0), B(2, 3), C(0, 3)
Coordinates of parallelogram PQRS are:
P(4, 3), Q(6, 1), R(6, 5), S(4, 7)
Coordinates of triangle KLM are:
K(10, 5), L(7, 7), M (10, 8).

4. State whether True or False. Correct that is false.
(i) A point whose x-coordinate is zero and y-coordinate is non-zero will lie on the y-axis.
(ii) A point whose y-coordinate is zero and x-coordinate is 5 will lie on y-axis.
(iii) The coordinates of the origin are (0, 0).
Solution:
(i) True
(ii) False, the point will lie on the x-axis with coordinates (5, 0).
(iii) True

Exercise 15.3 | Class 8th Mathematics

1. Draw the graphs for the following tables of values, with suitable scales on the axes.
   (a) Cost of apples
   
   (b) Distance travelled by car.
   
   (i) How much distance did the car cover during the period 7:30 am to 8 am?
   (ii) What was the time when the car had covered a distance of 100 km since its start?
   (c) Interest on deposits for a year.
   
   (i) Does the graph pass through the origin?
   (ii) Use the graph to find the interest on ? 2500 for a year.
   (iii) To get an interest of t 280 per year, how much money should be deposited?
   Solution:
   
   (b) (i) The distance covered by the car during the period 7:30 am to 8 am is (120 km – 100 km) = 20 km.
   (ii) At 7:30 am, the car had covered a distance of 100 km.
   
   (c) (i) Yes, the graph passes through the origin,
   (ii The interest on ₹ 2500 is ₹ 200 for 1 year.
   (iii) ₹ 3500 should be invested to earn the interest of ₹ 280.
   

2. Draw the graph for the following:

Solution:

Extra Questions | Class 8th Mathematics

Exercise 14.1 | Class 8th Mathematics

1. Find the common factors of the given terms.
   (i) 12x, 36
   (ii) 2y, 22xy
   (iii) 14pq, 28p²q²
   (iv) 2x, 3x², 4
   (v) 6abc, 24ab², 12a²b
   (vi) 16x³, -4x², 32x
   (vii) 10pq, 20qr, 30rp
   (viii) 3x²y³, 10x³y², 6x²y²z
   Solution:
   (i) 12x, 36
   (2 × 2 × 3 × x) and (2 × 2 × 3 × 3)
   Common factors are 2 × 2 × 3 = 12
   Hence, the common factor = 12

(ii) 2y, 22xy
= (2 × y) and (2 × 11 × x × y)
Common factors are 2 × y = 2y
Hence, the common factor = 2y

(iii) 14pq, 28p²q²
= (2 × 7 × p × q) and (2 × 2 × 7 × p × p × q × q)
Common factors are 2 × 7 × p × q = 14pq
Hence, the common factor = 14pq

(iv) 2x, 3x², 4
= (2 × x), (3 × x × x) and (2 × 2)
Common factor is 1
Hence, the common factor = 1 [∵ 1 is a factor of every number]

(v) 6abc, 24ab², 12a²b
= (2 × 3 × a × b × c), (2 × 2 × 2 × 3 × a × b × b) and (2 × 2 × 3 × a × a × b)
Common factors are 2 × 3 × a × b = 6ab
Hence, the common factor = 6ab

(vi) 16x³, -4x², 32x
= (2 × 2 × 2 × 2 × x × x × x), -(2 × 2 × x × x), (2 × 2 × 2 × 2 × 2 × x)
Common factors are 2 × 2 × x = 4x
Hence, the common factor = 4x

(vii) 10pq, 20qr, 30rp
= (2 × 5 × p × q), (2 × 2 × 5 × q × r), (2 × 3 × 5 × r × p)
Common factors are 2 × 5 = 10
Hence, the common factor = 10

(viii) 3x²y², 10x³y², 6x²y²z
= (3 × x × x × y × y), (2 × 5 × x × x × x × y × y), (2 × 3 × x × x × y × y × z)
Common factors are x × x × y × y = x²y²
Hence, the common factor = x²y².

2. Factorise the following expressions.
(i) 7x – 42
(ii) 6p – 12q
(iii) 7a² + 14a
(iv) -16z + 20z³
(v) 20l²m + 30alm
(vi) 5x²y – 15xy²
(vii) 10a² – 15b² + 20c²
(viii) -4a² + 4ab – 4ca
(ix) x²yz + xy²z + xyz²
(x) ax²y + bxy² + cxyz
Solution:
(i) 7x – 42 = 7(x – 6)
(ii) 6p – 12q = 6(p – 2q)
(iii) 7a² + 14a = 7a(a + 2)
(iv) -16z + 20z³ = 4z(-4 + 5z²)
(v) 20l²m + 30alm = 10lm(2l + 3a)
(vi) 5x²y – 15xy² = 5xy(x – 3y)
(vii) 10a² – 15b² + 20c² = 5(2a² – 3b² + 4c²)
(viii) -4a² + 4ab – 4ca = 4a(-a + b – c)
(ix) x²yz + xy²z + xyz² = xyz(x + y + z)
(x) ax²y + bxy² + cxyz = xy(ax + by + cz)

3. Factorise:
(i) x² + xy + 8x + 8y
(ii) 15xy – 6x + 5y – 2
(iii) ax + bx – ay – by
(iv) 15pq + 15 + 9q + 25p
(v) z – 7 + 7xy – xyz
Solution:
(i) x² + xy + 8x + 8y
Grouping the terms, we have
x² + xy + 8x + 8y
= x(x + y) + 8(x + y)
= (x + y)(x + 8)
Hence, the required factors = (x + y)(x + 8)

(ii) 15xy – 6x + 5y – 2
Grouping the terms, we have
(15xy – 6x) + (5y – 2)
= 3x(5y – 2) + (5y – 2)
= (5y – 2)(3x + 1)

(iii) ax + bx – ay – by
Grouping the terms, we have
= (ax – ay) + (bx – by)
= a(x – y) + b(x – y)
= (x – y)(a + b)
Hence, the required factors = (x – y)(a + b)

(iv) 15pq + 15 + 9q + 25p
Grouping the terms, we have
= (15pq + 25p) + (9q + 15)
= 5p(3q + 5) + 3(3q + 5)
= (3q + 5) (5p + 3)
Hence, the required factors = (3q + 5) (5p + 3)

(v) z – 7 + 7xy – xyz
Grouping the terms, we have
= (-xyz + 7xy) + (z – 7)
= -xy(z – 7) + 1 (z – 7)
= (-xy + 1) (z – 1)
Hence the required factor = -(1 – xy) (z – 7)

Exercise 14.2 | Class 8th Mathematics

1. Factorise the following expressions.
   (i) a² + 8a +16
   (ii) p² – 10p + 25
   (iii) 25m² + 30m + 9
   (iv) 49y² + 84yz + 36z²
   (v) 4x² – 8x + 4
   (vi) 121b² – 88bc + 16c²
   (vii) (l + m)² – 4lm. (Hint: Expand (l + m)² first)
   (viii) a⁴ + 2a²b² + b⁴
   Solution:
   (i) a² + 8a + 16
   Here, 4 + 4 = 8 and 4 × 4 = 16
   a² + 8a +16
   = a² + 4a + 4a + 4 × 4
   = (a² + 4a) + (4a + 16)
   = a(a + 4) + 4(a + 4)
   = (a + 4) (a + 4)
   = (a + 4)²

(ii) p² – 10p + 25
Here, 5 + 5 = 10 and 5 × 5 = 25
p² – 10p + 25
= p² – 5p – 5p + 5 × 5
= (p² – 5p) + (-5p + 25)
= p(p – 5) – 5(p – 5)
= (p – 5) (p – 5)
= (p – 5)²

(iii) 25m² + 30m + 9
Here, 15 + 15 = 30 and 15 × 15 = 25 × 9 = 225
25m² + 30m + 9
= 25m² + 15m + 15m + 9
= (25m² + 15m) + (15m + 9)
= 5m(5m + 3) + 3(5m + 3)
= (5m + 3) (5m + 3)
= (5m + 3)²

(iv) 49y² + 84yz + 36z²
Here, 42 + 42 = 84 and 42 × 42 = 49 × 36 = 1764
49y² + 84yz + 36z²
= 49y² + 42yz + 42yz + 36z²
= 7y(7y + 6z) +6z(7y + 6z)
= (7y + 6z) (7y + 6z)
= (7y + 6z)²

(v) 4x² – 8x + 4
= 4(x² – 2x + 1) [Taking 4 common]
= 4(x² – x – x + 1)
= 4[x(x – 1) -1(x – 1)]
= 4(x – 1)(x – 1)
= 4(x – 1)²

(vi) 121b² – 88bc + 16c²
Here, 44 + 44 = 88 and 44 × 44 = 121 × 16 = 1936
121b² – 88bc + 16c²
= 121b² – 44bc – 44bc + 16c²
= 11b(11b – 4c) – 4c(11b – 4c)
= (11b – 4c) (11b – 4c)
= (11b – 4c)²

(vii) (l + m)² – 4lm
Expanding (l + m)², we get
l² + 2lm + m² – 4lm
= l² – 2lm + m²
= l² – Im – lm + m²
= l(l – m) – m(l – m)
= (l – m) (l – m)
= (l – m)²

(viii) a⁴ + 2a²b² + b⁴
= a⁴ + a²b² + a²b² + b⁴
= a²(a² + b²) + b²(a² + b²)
= (a² + b²)(a² + b²)
= (a² + b²)²

2. Factorise.
(i) 4p² – 9q²
(ii) 63a² – 112b²
(iii) 49x² – 36
(iv) 16x⁵ – 144x³
(v) (l + m)² – (l – m)²
(vi) 9x²y² – 16
(vii) (x² – 2xy + y²) – z²
(viii) 25a² – 4b² + 28bc – 49c²
Solution:
(i) 4p² – 9q²
= (2p)² – (3q)²
= (2p – 3q) (2p + 3q)
[∵ a² – b² = (a + b)(a – b)]

(ii) 63a² – 112b²
= 7(9a² – 16b²)
= 7 [(3a)² – (4b)²]
= 7(3a – 4b)(3a + 4b)
[∵ a² – b² = (a + b)(a – b)]

(iii) 49x² – 36 = (7x)² – (6)²
= (7x – 6) (7x + 6)
[∵ a² – b² = (a + b)(a – b)]

(iv) 16x⁵ – 144x³ = 16x³ (x² – 9)
= 16x³ [(x)² – (3)²]
= 16x³(x – 3)(x + 3)
[∵ a² – b² = (a + b)(a – b)]

(v) (l + m)² – (l – m)²
= (l + m) – (l – m)] [(l + m) + (l – m)]
[∵ a² – b² = (a + b)(a – b)]
= (l + m – l + m)(l + m + l – m)
= (2m) (2l)
= 4ml

(vi) 9x²y² – 16 = (3xy)² – (4)²
= (3xy – 4)(3xy + 4)
[∵ a² – b² = (a + b)(a – b)]

(vii) (x² – 2xy + y²) – z²
= (x – y)² – z²
= (x – y – z) (x – y + z)
[∵ a² – b² = (a + b)(a – b)]

(viii) 25a² – 4b² + 28bc – 49c²
= 25a² – (4b² – 28bc + 49c²)
= (5a)² – (2b – 7c)²
= [5a – (2b – 7c)] [5a + (2b – 7c)]
= (5a – 2b + 7c)(5a + 2b – 7c)

3. Factorise the expressions.
(i) ax² + bx
(ii) 7p² + 21q²
(iii) 2x³ + 2xy² + 2xz²
(iv) am² + bm² + bn² + an²
(v) (lm + l) + m + 1
(vi) y(y + z) + 9(y + z)
(vii) 5y² – 20y – 8z + 2yz
(viii) 10ab + 4a + 5b + 2
(ix) 6xy – 4y + 6 – 9x
Solution:
(i) ax² + bx = x(ax + 5)

(ii) 7p² + 21q² = 7(p² + 3q²)

(iii) 2x³ + 2xy² + 2xz² = 2x(x² + y² + z²)

(iv) am² + bm² + bn² + an²
= m² (a + b) + n²(a + b)
= (a + b)(m² + n²)

(v) (lm + l) + m + 1
= l(m + 1) + (m + 1)
= (m + 1) (l + 1)

(vi) y(y + z) + 9(y + z) = (y + z)(y + 9)

(vii) 5y² – 20y – 8z + 2yz
= 5y² – 20y + 2yz – 8z
= 5y(y – 4) + 2z(y – 4)
= (y – 4) (5y + 2z)

(viii) 10ab + 4a + 5b + 2
= 2a(5b + 2) + 1(5b + 2)
= (5b + 2)(2a + 1)

(ix) 6xy – 4y + 6 – 9x
= 6xy – 4y – 9x + 6
= 2y(3x – 2) – 3(3x – 2)
= (3x – 2) (2y – 3)

4. Factorise.
(i) a⁴ – b⁴
(ii) p⁴ – 81
(iii) x⁴ – (y + z)⁴
(iv) x⁴ – (x – z)⁴
(v) a⁴ – 2a²b² + b⁴
Solution:
(i) a⁴ – b⁴ – (a²)² – (b²)²
[∵ a² – b² = (a – b)(a + b)]
= (a² – b²) (a² + b²)
= (a – b) (a + b) (a² + b²)

(ii) p⁴ – 81 = (p²)² – (9)²
= (p² – 9) (p² + 9)
[∵ a² – b² = (a – b)(a + b)]
= (p – 3)(p + 3) (p² + 9)

(iii) x⁴ – (y + z)⁴ = (x²)² – [(y + z)²]²
[∵ a² – b² = (a – b)(a + b)]
= [x² – (y + z)²] [x² + (y + z)²]
= [x – (y + z)] [x + (y + z)] [x² + (y + z)²]
= (x – y – z) (x + y + z) [x² + (y + z)²]

(iv) x⁴ – (x – z)⁴ = (x²)² – [(y – z)²]²
= [x² – (y – z)²] [x² + (y – z)²]
= (x – y + z) (x + y – z) (x² + (y – z)²]

(v) a⁴ – 2a²b² + b⁴
= a⁴ – a²b² – a²b² + b⁴
= a²(a² – b²) – b²(a² – b²)
= (a² – b²)(a² – b²)
= (a² – b²)²
= [(a – b) (a + b)]²
= (a – b)² (a + b)²

5. Factorise the following expressions.
(i) p² + 6p + 8
(ii) q² – 10q + 21
(iii) p² + 6p – 16
Solution:
(i) p² + 6p + 8
Here, 2 + 4 = 6 and 2 × 4 = 8
p² + 6p + 8
= p² + 2p + 4p + 8
= p (p + 2) + 4(p + 2)
= (p + 2) (p + 4)

(ii) q² – 10q + 21
Here, 3 + 7 = 10 and 3 × 7 = 21
q² – 10q + 21
= q² – 3q – 7q + 21
= q(q – 3) – 7(q – 3)
= (q – 3) (q – 7)

(iii) p² + 6p – 16
Here, 8 – 2 = 6 and 8 × 2 = 16
p² + 6p – 16
= p² + 8p – 2p – 16
= p(p + 8) – 2(p + 8)
= (p + 8) (p – 2)

Exercise 14.3 | Class 8th mathematics

1. Carry out the following divisions.
   (i) 28x⁴ ÷ 56x
   (ii) -36y³ ÷ 9y²
   (iii) 66pq²r³ ÷ 11qr²
   (iv) 34x³y³z³ ÷ 51xy²z³
   (v) 12a⁸b⁸ ÷ (-6a⁶b⁴)
   Solution:
   

2. Divide the following polynomial by the given monomial.
(i) (5x² – 6x) ÷ 3x
(ii) (3y⁸ – 4y⁶ + 5y⁴) ÷ y⁴
(iii) 8(x³y²z² + x²y³z² + x²y²z³) ÷ 4x²y²z²
(iv) (x³ + 2x² + 3x) ÷ 2x
(v) (p³q⁶ – p⁶q³) ÷ p³q³
Solution:

3. Work out the following divisions.
(i) (10x – 25) ÷ 5
(ii) (10x – 25) ÷ (2x – 5)
(iii) 10y(6y + 21) ÷ 5(2y + 7)
(iv) 9x²y²(3z – 24) ÷ 27xy(z – 8)
(v) 96abc(3a – 12) (5b – 30) ÷ 144(a – 4)(b – 6)
Solution:

4. Divide as directed.
(i) 5(2x + 1) (3x + 5) ÷ (2x + 1)
(ii) 26xy (x + 5)(y – 4) ÷ 13x(y – 4)
(iii) 52pqr(p + q) (q + r) (r + p) ÷ 104pq(q + r)(r + p)
(iv) 20(y + 4)(y² + 5y + 3) ÷ 5(y + 4)
(v) x(x + 1) (x + 2) (x + 3) ÷ x(x + 1)
Solution:

5. Factorise the expressions and divide them as directed.
(i) (y² + 7y + 10) ÷ (y + 5)
(ii) (m² – 14m – 32) ÷ (m + 2)
(iii) (5p² – 25p + 20) ÷ (p – 1)
(iv) 4yz(z² + 6z – 16) ÷ 2y(z + 8)
(v) 5pq(p² – q²) ÷ 2p(p + q)
(vi) 12xy(9x² – 16y²) ÷ 4xy(3x + 4y)
(vii) 39y³(50y² – 98) ÷ 26y²(5y + 7)
Solution:

Extra Questions | Class 8th Mathematics