MCQ Questions for Class 8 Science: Ch 6 Combustion and Flame

1. Fuel may be

(a) Solid only

(b) Solid,Liquid or gas

(c) Liquid only

(d) Gas only

► (b) Solid,Liquid or gas

2. Which of the following has the characteristics of a good fuel?

(a) Coke

(b) Butane

(c) Coal

(d) Kerosene

► (b) Butane

3. Combustion is a _____ chemical reaction:

(a) volatile

(b) exothermic

(c) endothermic

(d) none of the above

► (b) exothermic

4. The substances which give heat and light after combustion are called

(a) flame

(b) fuel

(c) combustion

(d) none of these

► (b) fuel

5. Cutting trees at large scale leads to :

(a) deforestation

(b) afforestation

(c) reforestation

(d) both deforestation & afforestation

► (a) deforestation

6. What kind of reaction is combustion?

(a) Reduction

(b) Redox

(c) Substitution

(d) Oxidation

► (d) Oxidation

7. Substance that burns in oxygen to produce heat and light is called :

(a) renewable

(b) non combustible

(c) combustible

(d) limitless

► (c) combustible

8. If a glass plate/slide is held into the luminous part of candle flame we see a circular blackish ring that represents:

(a) unburnt carbon particles

(b) formation of coal

(c) burnt carbon particles

(d) Both burnt carbon particles & formation of coal

► (a) unburnt carbon particles

9. Burning of LPG is an example of :

(a) slow combustion

(b) spontaneous combustion

(c) Both slow combustion & spontaneous combustion

(d) rapid combustion

► (d) rapid combustion

10. SI unit of the calorific value of a fuel is :-

(a) KJ/kg

(b) KW/kg

(c) N/kg

(d) KJ/g

► (a) KJ/kg

11. Burning of charcoal in a closed room will produce

(a) carbon dioxide

(b) nitrogen dioxide

(c) carbon monoxide

(d) all of these

► (c) carbon monoxide

12. Which of the following is an example of rapid combustion?

(a) Candle

(b) Cracker

(c) White phosphorus

(d) Sulphur

► (a) Candle

13. The gas which supports combustion of coal is :

(a) carbon dioxide

(b) oxygen

(c) nitrogen

(d) hydrogen

► (b) oxygen

14. Amount of heat energy produced on complete combustion of 1kg of fuel is called :

(a) energy value

(b) combustion value

(c) heat value

(d) calorific value

► (d) calorific value

15. Combustion is a

(a) chemical process

(b) physical process

(c) both of these processes

(d) none of these processes

► (a) chemical process

16. A material that burns is one that can combine quickly with :

(a) hydrogen

(b) oxygen

(c) carbon

(d) water

► (b) oxygen

17. Water works as a fire extinguisher by removing :-

(a) source of combustible substance

(b) heat

(c) oxygen

(d) both oxygen & heat

► (d) both oxygen & heat

18. What is the lowest temperature at which a substance starts burning called?

(a) Minimum temperature

(b) Maximum temperature

(c) Boiling temperature

(d) Ignition temperature

► (d) Ignition temperature

19. It is dangerous to extinguish fire caused by an electric short circuit with the use of :

(a) sand

(b) carbon dioxide

(c) water

(d) carbon monoxide

► (c) water

20. Substance that does not burn in air is :

(a) sand

(b) kerosene

(c) wood

(d) diesel

► (a) sand

21. No external heat is required to start :

(a) simultaneous combustion

(b) spontaneous combustion

(c) splendid combustion

(d) spreading fire combustion

► (b) spontaneous combustion

22. CNG and LPG are the examples of

(a) solid fuels

(b) liquid fuels

(c) gaseous fuels

(d) they are not fuels

► (c) gaseous fuels

23. Which of the following is a non- combustible substance?

(a) Coke

(b) Diamond

(c) Coal

(d) Wood

► (b) Diamond

24. The products of combustion are

(a) carbon dioxide and water

(b) oxygen and water

(c) only carbon dioxide

(d) only oxygen

► (a) carbon dioxide and water

Class 8 Science Chapter 6 Extra Questions and Answers Combustion and Flame

Extra Questions for Class 8 Science Chapter 6 Combustion and Flame with Answers Solutions

Combustion and Flame Class 8 Extra Questions Very Short Answer Type

Question 1.
Name the most common fuel used in homes.
Answer:
Liquefied Petroleum Gas. (LPG)

Question 2.
Name the most common fire extinguisher.
Answer:
Water

Question 3.
What are the states in which a fuel may exist?
Answer:
A fual may exist in solid, liquid or gaseous state.

Question 4.
ame any two combustible substances.
Answer:
Charcoal, wood

Question 5.
Does magnesium produce heat and light during its combustion?
Answer:
Yes, it does.

Question 6.
What acts as a fuel for our body?
Answer:
Food

Question 7.
Give two examples of non-combustible substances.
Answer:
Water, sand

Question 8.
How are heat and light produced in the sun?
Answer:
In the sun, heat and light are produced by nuclear reactions.

Question 9.
Where were matchsticks first used?
Answer:
Egypt

Question 10.
What are the three essential requirements for combustion?
Answer:
Fuel, air (to supply oxygen) and heat (to raise the temperature of the fuel beyond the ignition temperature).

Question 11.
What is the ignition temperature of phosphorus?
Answer:
25°C

Question 12.
What is the colour of an LPG flame?
Answer:
Blue

Question 13.
What type of process is combustion?
Answer:
A chemical process

Question 14.
Name an ideal fuel.
Answer:
Compressed Natural Gas (CNG)

Question 15.
What is the composition of the head of a matchstick?
Answer:
Antimony trisulphide and potassium chlorate.

Question 16.
Which part of a flame does a goldsmith blow for melting gold and silver?
Answer:
The goldsmith blows the outermost zone of a flame for melting gold and silver.

Question 17.
What is the unit for expressing the calorific value of a fuel?
Answer:
Kilojoules per kilogram (kJ/kg)

Question 18.
Comparing the calorific values of coal and petrol, state which fuel is better.
Answer:
The calorific value of coal is about 25,000 – 33,000 kJ/kg, whereas that of petrol is 45,000 kJ/kg. Hence, petrol is better tuel.

Question 19.
What is deforestation?
Answer:
The cutting down of trees on a large scale is termed as deforestation.

Question 20.
Give any two examples of carbon fuels.
Answer:
Coal, petroleum

Combustion and Flame Class 8 Extra Questions Short Answer Type

Question 1.
What does magnesium burn to form?
Answer:
Magnesium burns to form magnesium oxide and produces heat and light.

Question 2.
What does coal produce during its combustion?
Answer:
Coal produces carbon dioxide, heat and light during its combustion.

Question 3.
What is combustion?
Answer:
Combustion is a chemical process in which a substance reacts with oxygen to give off heat.

Question 4.
Define the ignition temperature of a fuel.
Answer:
The lowest temperature at which a fuel catches fire is called its ignition temperature.

Question 5.
How does a matchstick catch fire?
Answer:
By rubbing a matchstick against a rough surface (friction), it attains its ignition temperature and thus catches fire.

Question 6.
Why is sodium kept immersed in kerosene?
Answer:
Sodium has very low ignition temperature, i.e., it catches fire on coming in contact with air, so it is kept in kerosene.

Question 7.
What are combustible and non-combustible substances?
Answer:
Substances which undergo combustion are said to be combustible, whereas non-combustible substances are those which don’t burn.

Question 8.
What are inflammable substances? Give examples.
Answer:
The substances which have very low ignition temperature and can easily catch fire with a flame are called inflammable substances; e.g., LPG, petrol, alcohol, etc.

Question 9.
What is rapid combustion?
Answer:
When a substance burns instantly and produces a huge amount of heat and light, the combustion is called rapid combustion; e.g., the instant burning of LPG in a gas stove.

Question 10.
Define spontaneous combustion.
Answer:
A type of combustion in which the substance suddenly catches fire without the supply of heat or friction externally is called spontaneous combustion; e.g., forest fires.

Question 11.
Define explosion.
Answer:
A type of combustion during which a huge amount of heat and light is evolved with a boom, along with the production of gas, is known as explosion; e.g., the exploding of fireworks, i.e., crackers, etc.

Question 12.
What is flame?
Answer:
Flame is a region where the burning or combustion of gaseous substances take place.

Question 13.
Define fuel.
Answer:
Those substances which provide energy on burning are called ‘fuels’; e.g., coal, petroleum, LPG, etc.

Question 14.
Give two examples each of solid fuels, liquid fuels and gaseous fuels.
Answer:

• Solid fuels – Wood, cow dung, etc.
• Liquid fuels – Kerosene, petrol, etc.
• Gaseous fuels – Hydrogen, methane, etc.

Question 15.
Give two examples of fuels that are used to generate electricity.
Answer:
Two examples of fuels that are used to generate electricity are petrochemicals and coal.

Question 16.
Define calorific value.
Answer:
The amount of heat produced on burning one kilogram of fuel completely is called its calorific value.

Question 17.
60 kg of fuel was completely burnt for an experiment. The amount of heat energy was found to be 1,80,000 kJ. Calculate the calorific value of the fuel.
Answer:
Amount of fuel burnt = 60 kg
Amount of heat produced = 1,80,000 kJ

∴ Calorific value of the fuel is 3,000 kJ/kg.

Question 18.
Define dark zone of a flame.
Answer:
The innermost zone of a flame around the wick is called its dark zone. It is the least hottest zone comparatively to other.

Question 19.
Name the colours of the flames of following substances:
Barium, arsenic, sodium, magnesium
Answer:

Name of the substance	Colour of its flame
Barium	Pale/Apple green
Arsenic	Blue
Sodium	Yellow
Magnesium	White

Question 20.
Mention any three characteristics of a good fuel.
Answer:
Any three characteristics of a good fuel are following:

• It has high calorific value.
• It is very easy to transport.
• It is cheap, affordable and economic.

Question 21.
What is global warming?
Answer:
An increase in the average temperature of the earth’s atmosphere, especially a sustained increase that causes climatic changes, is termed as ‘global warming’.

MCQ Questions for Class 8 Science: Ch 5 Coal and Petroleum

1. Coal, Petroleum and natural gas are examples of

(a) Exhaustible Natural Resources

(b) Inexhaustible Natural Resources

(c) Expensive Resources

(d) None of the above

► (a) Exhaustible Natural Resources

2. What is the common name of petroleum?

(a) Black gold

(b) Yellow gold

(c) Green gold

(d) Blue gold

► (a) Black gold

3. By which of the given processes is coal formed?

(a) Carbonization

(b) Distillation

(c) Vaporization

(d) Evaporation

► (a) Carbonization

4. What does natural gas mainly consist of?

(a) C₂H₆

(b) CH₄

(c) C₃H₈

(d) C₄H₁₀

► (b) CH₄

5. When an oil well is drilled through rocks, which of the following comes out first?
(a) Coal gas
(b) Marsh gas
(c) Natural gas
(d) Carbon dioxide
► (c) Natural gas

6. Natural gas is a _____ resource :

(a) non renewable

(b) living

(c) renewable

(d) all the above

► (a) non renewable

7. What does gobar gas produced from animal and plant waste contain?

(a) Ethane

(b) Methane

(c) Propane

(d) Acetylene

► (b) Methane

8. What is the underlying principle based on which fractional distillation is carried out?

(a) Different densities of each fraction

(b) Different molecular weights of each fraction

(c) Different boiling points of each fraction

(d) Different melting points of each fraction

► (c) Different boiling points of each fraction

9. Where does natural gas occur?

(a) Above petroleum oil

(b) Below petroleum oil

(c) Along with petroleum oil

(d) Inside volcanic mountains

► (a) Above petroleum oil

10. A What are the most common sources of energy used in automobiles?

(a) Wood and coal

(b) Petroleum and diesel

(c) LPG and cow dung

(d) Natural gas and coal

► (b) Petroleum and diesel

11. When heated in air, coal burns to produce :

(a) Carbonates

(b) Carbon dioxide gas

(c) Oxygen gas

(d) Chlorofluorocarbons

► (b) Carbon dioxide gas

12. The purest form of carbon is

(a) Coal

(b) Charcoal

(c) Coke

(d) All of these

► (c) Coke

13. Coke is used to manufacture :

(a) coal tar

(b) producer gas

(c) natural gas

(d) biogas

► (b) producer gas

14. Coke is obtained from :

(a) destructive distillation of petroleum

(b) refining of coal

(c) destructive distillation of coal

(d) refining of petroleum

► (c) destructive distillation of coal

15. Fossil fuels are :

(a) renewable resource

(b) formed naturally

(c) formed artificially

(d) non combustible

► (b) formed naturally

16. At the petroleum refinery, crude oil mixture is :

(a) ultrafiltered

(b) filtered

(c) both filtered & ultrafiltered

(d) fractionated

► (d) fractionated

17. When coal burns in air then

(a) Carbon dioxide is formed

(b) Sulphur dioxide is formed

(c) Carbon monoxide is formed

(d) Hydrogen gas is formed

► (a) Carbon dioxide is formed

18. Where is kerosene mainly used?

(a) In laying down roads.

(b) As fuel in jet engines.

(c) In making water proof materials.

(d) In furnaces of industries.

► (b) As fuel in jet engines.

19. Coal was formed during :

(a) Devonian period

(b) Carboniferous period

(c) Silurian period

(d) Carbonian period

► (b) Carboniferous period

20. Coal is classified according to:

(a) its carbon content

(b) time taken in its formation

(c) layer of earth surface it is found

(d) its non carbon content

► (a) its carbon content

21. In fractional distillation of petroleum, where do the vapours with highest boiling point condense?

(a) In the upper-most portion

(b) In the lower-most portion

(c) In the middle portion

(d) Cannot be said

► (b) In the lower-most portion

22. Type of coal that can serve as good heating fuel for domestic purpose is :

(a) bituminous

(b) bauxite

(c) anthracite

(d) lignite

► (c) anthracite

23. Coal gas can be obtained from :

(a) burning coke with petroleum

(b) coal beds & destructive distillation of coal

(c) only fractional distillation of coal

(d) only destructive distillation of coal

► (b) coal beds & destructive distillation of coal

24. By what process is petroleum refined?

(a) Fractional distillation

(b) Destructive distillation

(c) Distillation

(d) All of the above

► (a) Fractional distillation

25. The youngest form of coal is:

(a) litter

(b) peat

(c) anthracite

(d) lignite

► (b) peat

26. PCRA stands for

(a) Public Conservations Research Association

(b) Petroleum Conservation Research Association

(c) Public Council of Research Association

(d) Partial Counting of Remaining Amendment

► (b) Petroleum Conservation Research Association

Class 8 Science Chapter 5 Extra Questions and Answers Coal and Petroleum

Extra Questions for Class 8 Science Chapter 5 Coal and Petroleum with Answers Solutions

Coal and Petroleum Class 8 Extra Questions Very Short Answer Type

Question 1.
Name some renewable sources of energy.
Answer:
Water, wind, solar.

Question 2.
Give some examples of fossil fuels.
Answer:
Coal, petroleum, natural gas.

Question 3.
Name the elements present in coal.
Answer:
Carbon, oxygen and sulphur.

Question 4.
Which are the two main techniques of mining?
Answer:
Surface mining and underground mining.

Question 5.
List four varieties of coal.
Answer:
Peat, lignite, bituminous, anthracite.

Question 6.
Name the process of conversion of wood into coal.
Answer:
Carbonisation

Question 7.
Mention the temperature at which destructive distillation is done.
Answer:
1000°C

Question 8.
When the crude oil is referred to be ‘sweet’?
Answer:
If the sulphur content is low.

Question 9.
Name the process of conversion of kerogen into gaseous hydrocarbons.
Answer:
Catagenesis

Question 10.
Name the country which is the leading producer of petroleum.
Answer:
Saudi Arabia

Question 11.
Name the gas that occurs over petroleum in reservoirs deep inside the earth.
Answer:
Natural gas

Question 12.
Expand PCRA.
Answer:
Petroleum Conservation Research Association.

Question 13.
Name two fractions of petroleum which are used as fuel.
Answer:
Petrol and diesel

Question 14.
What kind of pollution is caused by the burning of fossil fuels?
Answer:
Air pollution

Question 15.
Write the full form of LPG.
Answer:
Liquefied Petroleum Gas.

Question 16.
Which gas is produced when coal is burnt in air?
Answer:
Carbon dioxide

Question 17.
Can we use all our natural resources forever?
Answer:
No

Question 18.
What is the purest form of carbon?
Answer:
Coke

Question 19.
Where and when was the first oil well drilled?
Answer:
Pennsylvania, USA in 1859.

Question 20.
Name the places where natural gas is found in our country.
Answer:
Tripura, Rajasthan, Krishna Godavari Delta, Maharashtra, etc.

Coal and Petroleum Class 8 Extra Questions Short Answer Type

Question 1.
What is fuel?
Answer:
Anything that burns to produce energy in an efficient manner is called a fuel.

Question 2.
Define fossil fuels. Give examples.
Answer:
Natural fuels that are made up by burial of living organisms under deep down the earth for over a long period of time, are called fossil fuels. For example, coal, petroleum, natural gas.

Question 3.
What is coal? Write its two uses.
Answer:
Coal is a hard, black combustible substance that mainly contains carbon.
Uses:

• It is used as a fuel in homes and industry.
• It is used as a fuel at Thermal Power Plants for generating electricity.

Question 4.
Give a brief description about peat.
Answer:
Peat is the most inferior and softest form of coal. Its carbon content is very low. It has a large amount of moisture and is not much suitable to be used as fuel. Its carbon content is 20 – 25%.

Question 5.
Name three constituents of petroleum and write their uses also.
Answer:
The three constituents of petroleum are:
(a) petrol
(b) paraffin wax
(c) diesel
Uses:
(a) Petrol: It is used as a motor fuel and for dry cleaning.
(b) Paraffin wax: It is used for making ointments, candles, vaseline, etc.
(c) Diesel: It is used as a fuel for heavy motor vehicles and electric generators.

Question 6.
Explain about coal tar.
Answer:
It is produced when the gases are evolved due to heating of coal in water. It is a black-coloured, thick, viscous liquid. It has a pungent smell. It is itself a mixture of many compounds. We can get benzene, toluene, napthalene, phenol, etc., from coal tar.

Question 7.
Name two products that you obtain from the destructive distillation of coal. What is the residue left in’ this process? Give one main use of this residue.
Answer:
The two important products obtained from the destructive distillation of coal are: Coal gas and coal tar. The residue left in this process is coke. Coke is used mainly as a reducing agent in the extraction of metals.

Question 8.
Where do we get coal and how is it formed?
Answer:
We get coal deep in the earth’s crust in coal mines. It is formed by the slow decomposition of dead trees and other vegetable matter buried deep under the earth’s crust under high pressure and temperature.

Question 9.
Define the term ‘petrochemicals’.
Answer:
Petrochemicals are the substances obtained from petroleum and natural gas. They are used in the manufacture of detergents, fibres, polythene, etc.

Question 10.
What is CNG? What are its uses?
Answer:
CNG is short form of Compressed Natural Gas. Natural gas is stored under high pressure as CNG. CNG is used for power generation. It is now being used as a fuel for transport vehicles because it is less polluting. It is a cleaner fuel.

Coal and Petroleum Class 8 Extra Questions Long Answer Type

Question 1.
Explain about the varieties of coal.
Answer:
Depending upon the amount of carbon content, coal may be of four types:

• Peat: This is the most inferior and softest form of coal. Its carbon content is very low. It has a large amount of moisture and is not much suitable to be used as fuel.
• Lignite: Lignite is comparatively harder than peat, but still is very soft. Its carbon content is more than that of peat.
• Bituminous: Its carbon content is higher, as it is free from moisture and other impurities.
• Anthracite: This is the highest grade coal. This is also known as hard coal. It has maximum amount of carbon. It produces a very little smoke.

Question 2.
The burning of fossil fuels causes air pollution. Explain.
Answer:
The burning of fossil fuels causes a lot of air pollution.

The burning of coal produces gases like carbon dioxide, carbon monoxide, sulphur dioxide, etc., which can lead to undesirable changes in climate due to increase greenhouse effect.

The major air pollutants produced by the burning of petrol in automobiles are carbon monoxide, sulphur dioxide, unbumt hydrocarbons, etc. These pollutants are harmful for human beings and living organisms which causes breathing problems and skin diseases.

Question 3.
Write a short note on petroleum.
Answer:
Petroleum is the liquid form of fuel. It is also known as crude oil and found trapped between the layers of impervious rocks under the ground. It is a natural resource, which formed by the dead plants and animals in the sea. It is a dark coloured viscous liquid and like all other oils, it is lighter than water. It is a mixture of different hydrocarbons. It undergoes fractional distillation to yield petrol, kerosene, diesel and other chemicals used in manufacture of plastics.

Question 4.
How is the energy useful to us? Explain.
Answer:
We need energy in almost every field of our life. Without energy our life is impossible.
Some of the uses of energy are:

• We need energy of fuels to generate electricity and to run vehicles.
• We need energy to run our electrical appliances like refrigerator, TV, radio, computer, etc.
• We need energy at construction sites to construct houses, buildings, etc.
• We need energy to cook our food and other domestic use.
• We need energy (petrochemicals) for manufacturing fibres, plastics, paints, cosmetics, etc.
• All the factories, industries, agricultural devices depend on power supply to run the machines.

Question 5.
List the steps to conserve the resources.
Answer:
As we know, we all are dependent on the resources. But we should keep in mind that resources are limited in nature. If we misuse it, our future generation will have no resources. This is an alarming situation.
We can take following steps:

• We shbuld cook our food on low flame.
• Devices that consume less energy like CFLs and LED lights should be preferred.
• We should take care not to waste electricity.
• We should cover our cooking vessels while cooking.
• Instead of use of individual vehicles, use of public transport should be encouraged.
• Solar or tidal energy should be developed and encouraged.
• Dams should be use to generate electricity instead of burning coal or petroleum.
• Public awareness programmes should be conducted.

Materials Metals and Non Metals MCQ Questions Class 8 Science with Answers

Chapter 4

MATERIALS : METALS AND NON-METALS

Question. The property of metals by which they can be beaten into thin sheets is called ____
a) Ductility
b) Sheetability
c) Metallic
d) Malleability

Answer : D

Question. The property of metal by which it can be drawn into wires is called ______
a) Ductility
b) Sheetability
c) Metallic
d) Malleability

Answer : A

Question. The metal found in liquid state is
a) Iron
b) Aluminium
c) Mercury
d) Gold

Answer : C

Question. When a copper vessel is exposed to moist air for long, it acquires a dull green coating. The green material is a mixture of
a) Copper oxide and Copper Nitrate
b) Copper hydroxide & Copper Carbonate
c) Copper carbonate and Copper sulphate
d) Copper hydroxide and Copper Nitrate

Answer : B

Question. When sulphur dioxide is dissolved in water __________ is formed.
a) Sulphuric acid
b) Sulphoxy acid
c) Sulphurous acid
d) Sulphur trioxide

Answer : C

Question. Sodium metal is stored in
a) water
b) Kept under open air
c) alcohol
d) Kerosene

Answer : D

Question. Phosphorus is stored in
a) water
b) Kept under open air
c) alcohol
d) Kerosene

Answer : A

Question. Since metals produce ringing sounds, they are said to be ____.
a) Sound metal
b) Sonorous
c) Ring metal
d) malleable

Answer : B

Question. A substance which cannot be broken down further by chemical reactions, by cooling, heating, or by electrolysis, is called ______
a) Metal
b) Non Metal
c) Element
d) Compound

Answer : C

Question. They are not sonorous and are poor conductors of heat and electricity. These materials are
a) elements
b) Metals
c) Compound
d) Non metals

Answer : A

Question: When non-metals react with water then

• a) Non-metals do not react with water
• b) Hydrogen gas is formed
• c) Carbon dioxide gas is formed
• d) None of the options

Answer : A

Question: The metal which can be cut with a knife

• a) Sodium and potassium
• b) Barium and calcium
• c) Sodium and mercury
• d) Potassium and calcium.

Answer : A

Question: Metal oxides are of nature

• a) Basic
• b) Acidic
• c) Netural
• d) None of the options

Answer : A

Question: All metals are solids except

• a) Mercury
• b) Sodium
• c) Calcium
• d) Hydrogen

Answer : A

Question: Materials around us can be classified into

• a) Metals and non-metals
• b) Elements and compounds
• c) Acids and bases
• d) None of the options

Answer : A

Question: The non-metal which is liquid at room temperature is:

• a) Bromine
• b) Carbon
• c) Iodine
• d) Chlorine

Answer : A

Question: The metal which is stored in kerosene:

• a) Sodium
• b) Phosphorus
• c) Magnesium
• d) Magnesium

Answer : A

Question: Non-metals are:

• a) Generally solids and gases
• b) Generally liquids
• c) Generally gases
• d) Generally gases and liquids.

Answer : A

Question: The liquid metal at room temperature

• a) Mercury
• b) Bromine
• c) Sodium
• d) Gold

Answer : A

Question: The most reactive metal is:

• a) Potassium
• b) Iron
• c) Gold
• d) Zinc

Answer : A

Question: What is the product when sulphur reacts with oxygen?

• a) Sulphur dioxide
• b) Sulphurous acid
• c) Sulphuric acid
• d) Sulphur trioxide

Answer : A

Question: The solution of ash of magnesium ribbon is

• a) Basic
• b) Acidic
• c) Neutral
• d) All of the options

Answer : A

Question: Which metal is found in liquid state t room temperature?

• a) Hg
• b) Zn
• c) Fe
• d) Al

Answer : A

Question: The metals that produce ringing sounds, are said to be

• a) Sonorous
• b) Malleable
• c) Lustrous
• d) Hard

Answer : A

Question: The property of metal by which it can be drawn into wires is called

• a) Ductility
• b) Decorating
• c) Malleability
• d) Conductivity

Answer : A

Question: Which one of the following is a good conductor of electricity?

• a) Iron
• b) Plastic
• c) Wood
• d) Glass

Answer : A

Question: All materials shown property of malleability expect

• a) Graphite
• b) Iron
• c) Aluminium
• d) Silver

Answer : A

Question: The property of metals by which they can be beaten in to thin sheets is called

• a) Malleability
• b) Ductility
• c) Conduction
• d) Expansion

Answer : A

Question: Which one of the following is metal?

• a) Na
• b) N
• c) O
• d) C

Answer : A

Question: Which one of the following is non metal?

• a) N
• b) Fe
• c) Al
• d) Zn

Answer : A

Materials: Metals and Non-Metals Class 8 Extra Questions Very Short Answer Type

Question 1.
Name some common metals.
Answer:
Copper, aluminium, iron, silver, gold, etc.

Question 2.
Name some common non-metals.
Answer:
Hydrogen, oxygen, carbon, sulphur, phosphorus, etc.

Question 3.
Give examples of metalloids.
Answer:
Antimony, arsenic, silicon, boron, etc.

Question 4.
Name the property due to which metals shine.
Answer:
Lustre

Question 5.
Name two metals which are soft enough to be cut.
Answer:
Potassium and sodium

Question 6.
Name the property due to which metals can be beaten into thin sheets.
Answer:
Malleability

Question 7.
Which non-metal does conduct heat and electricity?
Answer:
Carbon

Question 8.
Name the property due to which metals can be drawn into wires.
Answer:
Ductility

Question 9.
Name the metal and non-metal which occur in liquid state.
Answer:
Mercury (metal), bromine (non-metal).

Question 10.
Due to which property a bell rings?
Answer:
Sonority

Question 11.
Generally, non-metals are non-lustrous. Name one non-metal which is lustrous.
Answer:
Iodine

Question 12.
State the property of non-metals due to which phosphorus is kept in water.
Answer:
Non-metals do not react with water.

Question 13.
Why some metals displace other metals from their solution?
Answer:
Because of being more reactive than the metals which they displace.

Question 14.
Which metal is used for wrapping food items?
Answer:
Aluminium

Question 15.
Which metal is more reactive: Iron or zinc?
Answer:
Zinc

Question 16.
Which metal is less reactive: Copper or zinc?
Answer:
Copper

Question 17.
Name one metal which does not react with dilute hydrochloric acid.
Answer:
Copper

Question 18.
Whose oxides are basic in nature: Metal or non-metal?
Answer:
Metal

Question 19.
Whose oxides are acidic: Metal or non-metal?
Answer:
Non-metal4

Question 20.
Name two metals which do not react with oxygen even at high temperature.
Answer:
Gold and silver

Question 21.
Classify the following into metals and non-metals:
Copper, iron, graphite, sulphur, aluminium, oxygen
Answer:
Metals: Copper, iron, aluminium
Non-metals: Graphite, sulphur, oxygen

Question 22.
Name two physical properties of metals.
Answer:
Malleability and sonority

Question 23.
What happens when metals react with oxygen?
Answer:
Metal oxides are formed.

Question 24.
What happens when magnesium is burnt in air?
Answer:
Magnesium burns with a white dazzling flame and a white powdery magnesium oxide is formed.

Question 25.
What happens when metals react with water?
Answer:
Metals produce their hydroxides or oxides and hydrogen.

Materials: Metals and Non-Metals Class 8 Extra Questions Short Answer Type

Question 1.
What is a metal?
Answer:
Substances having characteristic properties like malleability, ductility, sonority, conductivity, lustre, – and solidness are called metals. For example, aluminium, copper, zinc, iron, etc.

Question 2.
What are non-metals?
Answer:
Substances which are soft and dull, i.e., non-lustrous, non-sonorous, non-ductile, non-malleable and poor conductor of heat and electricity are called non-metals. For example, oxygen, hydrogen, sulphur, etc.

Question 3.
Mention the physical properties of metals.
Answer:
Physical properties of metals are:

• Malleable
• Lustre
• Sonorous
• Ductile
• Solid
• Good conductor of heat and electricity

Question 4.
What are the physical properties of non-metals?
Answer:
The physical properties of non-metals are:

• Non-malleable
• Non-sonorous
• Non-lustrous, i.e., dull in appearance
• Non-ductile
• Poor conductor of heat and electricity

Question 5.
Explain the term ‘malleability’ with suitable examples.
Answer:
Malleability is the property of metals due to which they can be beaten into thin sheets. For example, if we beat or hammer any metal like aluminium, zinc, iron, copper, etc., it become longer and larger but does not break. Thin sheets can be obtained by this process.

Question 6.
What is ductility? Explain with examples.
Answer:
Ductility is one of the properties of metals due to which they can be drawn into wires. For example, aluminium and copper are drawn into wires and used for electrical and different purposes.

Question 7.
Why aluminium is used for wrapping of food items?
Answer:
Aluminium is a metal and hence possesses malleability property. It can be beaten into thin sheets and can be folded into any shape. It is cheaper than other malleable metals and does not react with food items. That is why it is used as wrapping materials for food items.

Question 8.
Why metals are used in ringing bells?
Answer:
Metals have sonority. Due to this property, they can produce ringing sounds. That is why metals are used in ringing bells.

Question 9.
What are the differences between metals and non-metals? Explain on the basis of their physical properties.
Answer:

• Metals are malleable and give thin sheets after hammering whereas non-metals are brittle and give no sheets.
• Metals are ductile and can be drawn into wires whereas non-metals are non-ductile and can’t be drawn into wires.
• Metals are sonorous and used in ringing bells whereas non-metals are non-sonorous and cannot be used in ringing bells.
• Metals are good conductors of heat and electricity while non-metals are poor conductors.

Question 10.
What happen when a copper vessel is exposed to moist air for long? Also write the equation.
Answer:
When a copper vessel is exposed to moist air for long, it acquires a dull green coating. This green material is a mixture of copper hydroxide [Cu(OH)₂] and copper carbonate (CuCO₃). The reaction is as follows:

Question 11.
What happens when a magnesium ribbon is heated in presence of air?
Answer:
When a magnesium ribbon is heated in presence of air, it burns with a white dazzling flame and a white powdery magnesium oxide is formed.

Question 12.
How do metals and non-metals react with water?
Answer:
Metals produce their hydroxides or oxides and hydrogen when they react with water. Sodium and potassium react with cold water along with the production of a large amount of heat. Magnesium react with boiling water and iron with steam. Gold, silver and platinum do not react with water. Non-metals do not react with water.

Question 13.
With the help of equations, explain the reaction of non-metals with oxygen.
Answer:
Non-metals react with oxygen to form acidic oxides. But most of the non-metals reacts with oxygen on ignition.
The equations follow as:

Question 14.
How do metals and non-metals react with acids?
Answer:
Metals react with acids to form respective salts along with evolution of hydrogen gas that burns with a pop sound. The equation are as follows:

There are some metals like copper, silver, gold and platinum that do not liberate hydrogen with acids. Generally, non-metals do not react with acids.

Question 15.
How do metals and non-metals react with bases?
Answer:
Most of the metals do not react with bases. However, some metals like aluminium, lead and zinc react with strong bases like sodium hydroxide (NaOH) to make complex salts and hydrogen.
Generally, non-metals do not react with bases. Sometimes some complex reactions take place between non-metals and bases.

Question 16.
What is a displacement reaction? Give one example.
Answer:
A chemical reaction in which a more reactive metal displaces a less reactive metal is called displacement , reaction. For example, when zinc (Zn) reacts with copper sulphate (CuSO₂), zinc replaces copper being it more reactive than copper. The equation is

Materials: Metals and Non-Metals Class 8 Extra Questions Long Answer Type

Question 1.
Distinguish between metals and non-metals on the basis of their physical properties.
or
Compare the physical properties of metals and non-metals.
Answer:
Difference between metals and non-metals on the basis of their physical properties.

Physical Properties		Non-metals
1. Malleability	Metals are malleable, i.e., they can be beaten into thin sheets. Exception: Mercury	Non-metals are non- malleable. They are broken into pieces when hammered. Hence they are also called brittle.
2. Sonority	Metals are sonorous, i.e., they pro­duce ringing sound when struck.	Non-metals are non-sonorous.
3. Ductility	Metals are ductile, i.e., they can be drawn into wires. Exception: Mercury	Non-metals are non-ductile.
4. Lustre	Metals are lustrous, i.e., they are shiny.	Non-metals are non-lustrous, i.e., they are dull in appearance. Exception: Graphite and iodine.
5. Hardness or solidness	Metals are hard except sodium and potassium.	Non-metals are soft except diamond.
6. Conductivity	Metals are good conductor of heat and electricity.	Non-metals are poor conductor of heat and electricity. Exception: Graphite is a non-con­ductor of heat and electricity.
7. Density	Metals are of high density except lithium.	Non-metals are of low density.
8. Melting and boiling points.	Metals have high melting and boiling points.	Non-metals have low melting and boiling points except graphite.

Question 2.
Distinguish between metals and non-metals on the basis of their chemical properties.
or
Compare between metals and non-metals on the basis of their chemical properties.
Answer:
Difference between metals and non-metals on the basis of their chemical properties.

Chemical Properties	Metals	Non-metals
1. Reaction with oxygen	Metals react with oxygen to form basic oxides which form bases when dissolve in water.	Non-metals react with oxygen to form acidic oxides which form acids when dissolve in water.
2. Reaction with water	Metals react with water to form their oxides or hydroxides.	Non-metals do not react with water.
3. Reaction with acids	Metals react with acids to produce respective salts along with evolution of hydrogen gas. Some metals like Cu, Ag, Au, etc., do not liberate hydrogen gas.	Non-metals do not react with acids except sulphur which react with hot, concentrated acid.
4. Reaction with bases	Most of the metals do not react with bases. However, some metals like Al, Pb, Zn react with strong bases like NaOH to form complex salts and hy­drogen gas.	Generally, non-metals do not react with bases. Sometimes, some complex reactions take place between non­metals and bases.

Question 3.
Explain chemical properties of metals with examples.
Answer:
(i) Reaction with oxygen or air: Metals react with oxygen to form basic oxides.
Some metals like potassium and sodium react vigorously with oxygen. For example,

Some noble metals like gold, silver and platinum do not react with oxygen. Iron (Fe) and copper (Cu) get rusted when react in presence of oxygen and water (moist air).

(ii) Reaction with water: Metals react with water to form their oxides or hydroxides. Gold, silver and platinum do not react with water. Some metals like sodium, potassium react vigorously with water. For example,

(iii) Reaction with acids: Metals react with acid to form their salts followed by evolution of hydrogen gas. For example,

Some metals like gold, copper, silver, etc., do not liberate hydrogen gas with acids.

(iv) Reaction with bases: Most of the metals do not react with bases. However some metals like aluminium, zinc and lead react with strong bases like sodium hydroxide to make complex salts and produce hydrogen.

(v) Displacement reactions: More reactive metals displace less reactive metals. For example,

In the above reactions, zinc (Zn) and magnesium (Mg) are more reactive than copper (Cu), hence they replace copper from its solution.

Question 4.
Explain with suitable examples the chemical properties of non-metals.
Answer:
Reaction with oxygen: Non-metals react with oxygen to form acidic oxides. But most of them do this on ignition. For example,

They form negative ions and are good oxidising agents.
Reaction with water: Non-metals do not react with water.
Reaction with acids and bases: Generally, non-metals do not react with acids and bases. How¬ever, sometimes some complex reactions take place between non-metals and bases.

Question 5.
What are main uses of metals?
or
How are metals useful to us?
Answer:
Metals are very useful to us in many ways. For example,
(i) Due to their thermal and electrical conductivity, metals are use to make utensils, cooking vessels, wires and appliances. For example, copper and aluminium are mainly used for these purposes.

(ii) Metals like iron and steel are used in various tools, machinery, pipes, rods, sheets, doors, windows, construction works like bridges, roads, buildings, etc.

(iii) Aluminium is used as packaging and wrapping materials. It is also used in aircrafts and automobiles, etc.

(iv) Metals like gold, silver and platinum are used to make jewellery and other decorating items.

(v) Zinc is used in galvanisation and dry cell and chromium in electroplating.

(vi) Lead is used in making electrodes and batteries.

Question 6.
What are the main uses of non-metals?
or
How are non-metals useful to us?
Answer:
Like metals, non-metals also play an important role in our lives. They help us in many ways. For example,
(i) We breathe oxygen which is the basis of life of all living things including human beings. Without it, no living beings can exist alive on this earth.

(ii) CO₂ which is a non-metal oxide is essential for plants to carry out photosynthesis.

(iii) Non-metals like nitrogen and phosphorus are used in fertilisers for better yield of plant. Phosphorus is used in manufacturing of matchsticks and fireworks.

(iv) Non-metal like iodine is used in the purple coloured solution applied on wounds. Sulphur is also used in preparing skin medicines and making ointment due to its fungicidal properties.

(v) Non-metal like chlorine is used in water purification process. Due to its bleaching properties it is used to make bleaching powder.

(vi) Carbon, a non-metal, is used in most of the fuels.

Question 7.
What is reactivity series? Suggest an activity to arrange sodium, magnesium and copper in the order of their decreasing reactivity.
Answer:
Reactivity series is an arrangement of metals in decreasing order of their reactivity from highest to lowest. The metals occupying the higher positions in the activity series are more reactive in displacing the other metals lying below it from the solutions of their salts.

The activity series is a useful guide for predicting the products of metal displacement reactions. For example, placing a strip of zinc metal in a copper (II) sulphate solution will produce metallic copper and zinc sulphate, since zinc is above copper on the series.

A trip of copper placed into a zinc sulphate solution will not produce an appreciable reaction, because copper is below zinc on the series and can’t displace zinc ions from solution.

Activity to arrange sodium, magnesium and copper in the order of their decreasing reactivity:
(i) Take a pinch of sodium with a forceps and place in a beaker containing water. You will notice that sodium reacts vigorously.

(ii) Take a small piece of magnesium ribbon and add warm water to it. Magnesium reacts with warm water to form magnesium oxide and hydrogen gas. Magnesium reacts very slowly with cold water.

(iii) Take small pieces of copper turnings and add warm water to it. It doesn’t react with warm water also.

Hence, increasing order of reactivity is Na > Mg> Cu.

Materials: Metals and Non-Metals Class 8 Extra Questions HOTS

Question 1.
Why does calcium float in water?
Answer:
The hydrogen gas formed on adding calcium to water sticks to the surface of calcium solid and make it float in water.

Question 2.
Zinc sulphate forms a colourless solution in water. Will you observe any colour on adding copper turning in it?
Answer:
No, because copper is less reactive than zinc and will not be able to displace zinc from its salt solution

Question 3.
A doctor prescribed a tablet to a patient suffering from iron deficiency. The tablet does not look like iron. Explain.
Answer:
The tablet is not made of iron metal, instead it contains a salt of iron.

Question 4.
Ram stored copper sulphate solution in a container made of iron. He observed certain changes after few hours. Can you tell what changes did he observed?
Answer:
Blue colour solution of copper sulphate has changed to green colour of ferrous sulphate. The iron container was found to be corroded from many places. A red powdery deposit of copper sulphate was found on the iron container.

Question 5.
Imagine that gold is reactive like copper. Will it be still wanted? Why or why not?
Answer:
If gold becomes reactive like copper then its use in ornaments will decline. This is because due to its increase reactivity it will lose its shine frequently which in turn will reduce its demand.

Materials: Metals and Non-Metals Class 8 Extra Questions Value Based (VBQs)

Question 1.
Gold is a very precious metal. Pure gold is very soft and is thus not suitable for making jewellery. It is alloyed with either silver or copper to make it hard. But some jewellers mix a large quantity of copper and silver in gold to earn more profit.

(a) What precautions should you take while purchasing gold jewellery?
(b) What standard you must see on gold ornaments?
(c) What value of shopkeeper’s are shown here?
Answer:
(a) We must see the carat of gold jewellery, current price and BIS hallmark on it.
(b) BIS hallmark.
(c) Some shopkeeper’s are greedy, mean, cheater and money minder.

Question 2.
Mercury is largely used in thermometers to measure the temperature. It is a very dangerous metal as its density is very high. If it get into the food chain, it leads to mercury poisoning.
(a) What two precautions you must take while handling equipments containing mercury?
(b) Why mercury is used in thermometers?
(c) Can you suggest other alternatives to mercury thermometers?
Answer:
(a)

• We must handle the equipments carefully and firmly.
• If there is a mercury spill, we must leave the area immediately and inform our parents or teachers.

(b) Mercury is a good conductor of heat. Hence, the slightest change in temperature i° otable when it is used in a thermometer.
(c) Digital thermometer and spirit thermometer.

MCQ Questions for Class 8 Science: Ch 3 Synthetic Fibres and Plastics

1. Polythene and PVC are examples of

(a) Bio degradable substance

(b) Thermosetting plastics

(c) Thermoplastics

(d) Rayon

► (c) Thermoplastics

2. _____ is blended with wool for making carpets.

(a) Rayon

(b) Nylon

(c) Polystyrene

(d) Polyester

► (a) Rayon

3. Fabric is made of

(a) steel

(b) fibre

(c) paper

(d) none of these

► (b) fibre

4. The raw materials used in making nylon

(a) Wood pulp

(b) Cellulose

(c) Coal, water, air

(d) All of these

► (c) Coal, water, air

5. Which of the following set of features belong to thermoplastics ?

(a) soft and brittle

(b) hard and strong

(c) hard and less brittle

(d) soft and less brittle

► (d) soft and less brittle

6. Which of the following is a thermosetting plastic ?

(a) Nylon

(b) PTFE

(c) Polyester

(d) Melamine

► (d) Melamine

7. First synthetic fibre formed from natural material is:

(a) Rayon

(b) Acrylon

(c) Nylon

(d) Polyester

► (a) Rayon

8. Statement incorrect for synthetic fibres is/are:

(a) non-biodegradable

(b) very expensive

(c) long lasting

(d) all the above

► (b) very expensive

9. The first man-made fibre is

(a) nylon

(b) polyester

(c) rayon

(d) cotton

► (c) rayon

10. Why is it not advisable to wear clothes made up of synthetic fibres in hot and humid weather?

(a) Synthetic fibres catch fire very easily.

(b) Synthetic fibres do not absorb sweat.

(c) Synthetic fibres stick to the body.

(d) Both (b) and (c).

► (d) Both (b) and (c).

11. A man- made fibre obtained from natural source is :

(a) Acrylic

(b) Nylon

(c) Rayon

(d) Polyester

► (c) Rayon

12. Fibre obtained by chemical treatment of wood pulp is called ___________.    

(a) Natural silk

(b) Rayon

(c) Nylon

(d) Polyester

► (b) Rayon

13. When plastics are burnt they release:

(a) oxygen gas

(b) biogas

(c) toxic gases

(d) nitrogen gas

► (c) toxic gases

14. The strongest fibre is called:

(a) rayon

(b) nylon

(c) acrylic

(d) none of these

► (b) nylon

15. Remoulding can be done of :

(a) Polyvinyl chloride

(b) Bakelite

(c) Melamine

(d) Formaldehyde

► (a) Polyvinyl chloride

16. Raw materials for the synthetic fibres are derived from :

(a) petroleum products

(b) plant products

(c) animal products

(d) only coal

► (a) petroleum products

17. The lightweight plastic material is :

(a) Polypropylene

(b) Polythene

(c) Bakelite

(d) Polyester

► (a) Polypropylene

18. The small units used in making synthetic fibres are:

(a) molecules

(b) polymers

(c) cells

(d) none of these

► (b) polymers

19. Which of the following is not a characteristic of plastics?

(a) Plastics are poor conductors of heat.

(b) Plastics are insoluble in water.

(c) Plastics are non-inflammable.

(d) Plastics do not react with water and air.

► (c) Plastics are non-inflammable.

20. The oldest synthetic plastic is :

(a) Polyester

(b) Bakelite

(c) Melamine

(d) Polythene

► (b) Bakelite

21. Plastics are generally made from

(a) coal

(b) plant products

(c) kerosene

(d) petroleum

► (d) petroleum

22. Which of the following is used for making stockings and parachutes?

(a) Bakelite

(b) Wool

(c) Nylon

(d) Cotton

► (c) Nylon

23. Which of the following materials is the best for making garments and jackets that can be used in wet or damp environment?

(a) Polyester

(b) Wool

(c) Cotton

(d) None of these

► (a) Polyester

24. The fibre made up by the chemical treatment of wood pulp is

(a) Rayon

(b) Nylon

(c) Polyester

(d) None of these

► (a) Rayon

Synthetic Fibres and Plastics Class 8 Extra Questions Short Answer Questions

Question 1.
What are polymers?
Answer:
Polymers are compounds that are made up of same, small repeating units, joined together through bonds in a linear pattern.

Question 2.
What is cellulose?
Answer:
Cellulose is a polymer made up of large number of glucose units.

Question 3.
List the two ways in which synthetic fibres can be synthesised.
Answer:
Synthetic fibres may be synthesised by two ways:

• By regenerating them from natural fibres, like in rayon.
• By using entirely chemicals and chemical reactions, like in nylon.

Question 4.
What is rayon?
Answer:
Rayon is a man-made fibre which is produced by the chemical processing of wood pulp, i.e., a natural substance.

Question 5.
List two uses of rayon.
Answer:
The two uses of rayon are:

• It is used to make apparels like shirts, blouses, etc.
• It is used to make furnishings and upholstery.

Question 6.
List any two properties of rayon.
Answer:
The two properties of rayon are:

• Rayon is a versatile fibre.
• It can be dyed in different colours.

Question 7.
Draw a diagram to show the:
(a) linear arrangement of units in plastic.
(b) cross-linked arrangement of units in plastic.
Answer:

Question 8.
Write some advantages of synthetic fibres.
Answer:
Advantages of synthetic fibres are:

• Synthetic fibres are strong and durable.
• They do not shrink.
• They are moth and insect resistant.

Question 9.
What are plastics?
Answer:
Plastics are those substances which are mostly synthetic in nature, obtained mainly from petrochemi¬cal sources and can be moulded into different shapes.

Question 10.
What is plasticity?
Answer:
Plasticity is the property of materials by which they can be moulded into any shape.

h

Question 11.
What are thermosetting plastics?
Answer:
Thermosetting plastics are those which when moulded once, cannot be softened again and lose their plasticity.

Question 12.
List any three properties of plastics.
Answer:
The three properties of plastics are:

• They are non-corrosive in nature.
• They are light in weight and durable.
• They do not conduct heat.

Question 13.
What are the uses of polyester?
Answer:
The uses of polyester are:

• It is used in making home furnishings and apparels.
• Polyester is used for finishing on guitars and pianos.

Question 14.
Why is it advised not to wear synthetic clothes while working in a laboratory or working with fire in the kitchen?
Answer:
The synthetic fibres melt on heating. This is actually a disadvantage with synthetic fibres. If the cloth catches fire it can be very disastrous. The fabric melts and sticks to the body of the person wearing it. It is therefore advised not to wear synthetic clothes while working in a laboratory or working with fire in the kitchen.

Question 15.
Write some properties and uses of melamine.
Answer:
Melamine is a versatile material. It resists fire and can tolerate heat better than other plastics. It is used for making floor tiles, kitchenware and fabrics which resist fire.

Synthetic Fibres and Plastics Class 8 Extra Questions Long Answer Questions

Question 1.
Describe about nylon. Write its uses and properties.
Answer:
Nylon is the strongest amongst all the synthetic fibres. It is fully synthetic polymer which is prepared from coal, water and air. It is a polymer of amides. It was made in 1931 for the first time. It was used as a supplement of silk when silk got deficient during World War II for many military applications. Uses of Nylon

• Nylon is used in toothbrushes, combs, etc.
• It is used to make parachutes, tents, ropes, etc.
• It is used to make socks and stockings as it is elastic.
• It is widely used for making clothes, carpets, etc.

Properties of Nylon

• It melts on heating.
• It absorbs less water.
• It is resistant to moths and fungi.
• It has high tensile strength.
• It is durable.

Question 2.
Write the advantages of synthetic fibres.
Answer:
Synthetic fibres has many advantages as compared to natural fibres. Some of them are as follows:

• They are very strong and durable.
• They are cheaper in cost as compared to natural fibres.
• They absorb less water and are quick to dry.
• They do not shrink.
• They are very useful for saving our trees and animals as they are made up of chemicals.
• They are moth and insect resistant.

Question 3.
List the common varieties of polyester. Also mention the natural fibres which are used for blending to enhance their properties.
Answer:
Polyester could be blended with natural fibres to enhance its properties. The common varieties of polyester are:

• PET (Polyethylene terephthalate)
• Terrycot: It is made by blending polyester and cotton.
• Terrysilk: It is made by blending polyester iaiid silk.
• Terrywool: It is made by blending polyester and wool.

Question 4.
Explain the properties of plastics.
Answer:
Plastics are those substances which are mostly synthetic in nature.
Following are the properties of plastics:

• Plastics are non-corrosive in nature, i.e., they do not react easily with air and water. They are unaffected by most of the chemicals in normal conditions.
• Plastics are the bad conductor of heat. They do not get heated up like metals.
• Plastics are non-biodegradable, i.e., they do not get decomposed by microorganisms.
• Plastics are very durable.

Question 5.
‘Plastics are hazard to environment’. Explain this statement.
Answer:
Yes, plastics are hazard to environment. They make versatile materials but are very dangerous to the environment. Plastics are non-biodegradable in nature. It takes more than 100 years to decompose. If use of plastics are not reduced, our earth would turn into a big garbage bin.
The major problems due to plastics are:

• If plastics are burnt, they evolve poisonous gases. These gases destroys the ozone layer of the earth and also pollute the environment.
• If the plastics are disposed in drains, they choke the drains causing waterlogging.
• If these plastics are swallowed by the innocent animals along with their food, they harm their di-gestive system which leads to their death.
• They are manufactured by the consumption of a large amount of petroleum.

Question 8.
List the strategies for plastic waste management.
Answer:
Some of the strategies for plastic waste management are:

• We should use paper bags and jute bags instead of using plastic bags.
• The government should ban the use of plastic bags.
• Plastics should be recycled to make other useful products which do not harm the environment.
• We should use a special garbage bins to dispose plastic wastes.
• We should not throw plastic wastes in water bodies.
• Practicing 4R’s principle, i.e., Reuse, Recycle, Reduce and Recover should be encouraged.

MCQ Questions for Class 8 Science: Ch 2 Microorganisms: Friend and Foe

1. Identify bacteriophage.

(a) Algae

(b) Virus

(c) Protozoa

(d) Fungi

► (b) Virus

2. Microbiology is the study of :

(a) Useful products prepared from microbes

(b) Parts of living organisms

(c) Microbes

(d) Diseases caused by microorganisms

► (c) Microbes

3. _______ are the agents that act as carriers of a pathogen and spread diseases.

(a) Microbes

(b) Parasites

(c) Vectors

(d) DNA

► (c) Vectors

4. Rhizobium bacteria

(a) Help in digestion

(b) Cause diseases

(c) Help in nitrogen fixation

(d) All of these

► (c) Help in nitrogen fixation

5. Malaria is caused by

(a) Protozoa

(b) Virus

(c) Algae

(d) Bacteria

► (a) Protozoa

6. Scientists who study microorganisms are called

(a) microbiologists

(b) microscopists

(c) microorganists

(d) microtypist

► (a) microbiologists

7. The moist bread becomes mouldy after a few days when it is left in a container with a cover. Which of the following conditions favour the growth of the fungus?

(a) Absence of water

(b) Absence of light

(c) Presence of sunlight

(d) Presence of carbon dioxide

► (b) Absence of light

8. What process takes place when yeast is added to grape juice and left for a week?

(a) Decomposition

(b) Fermentation

(c) Distillation

(d) Oxidation

► (b) Fermentation

9. Which is a fungal disease in human?

(a) amoebiasis

(b) tuberculosis

(c) anthrax

(d) Athlete’s foot

► (d) Athlete’s foot

10. Which of the following disease causing pathogens is / are carried by mosquitoes?

(a) Dengue fever

(b) Malaria

(c) Cholera

(d) Both (A) and (B)

► (d) Both (A) and (B)

11. Which of the following terms is given to the microorganisms that cause diseases?

(a) Antigens

(b) Antibodies

(c) Pathogens

(d) Vectors

► (c) Pathogens

12. Amoeba belongs to

(a) Algae

(b) Fungi

(c) Protozoa

(d) Virus

► (c) Protozoa

13. Yeast is not used in the preparation of :

(a) bread

(b) alcohol

(c) dhokla

(d) antibiotic

► (d) antibiotic

14. Microorganisms are :

(a) saprophytes

(b) autotrophs

(c) autotrophs & heterotrophs

(d) hetrotrophs

► (c) autotrophs & heterotrophs

15. Which of the following can affectively prevent the ringworm disease?

(a) Vaccination

(b) Vector control

(c) Improving personal hygiene

(d) Using antibiotics

► (c) Improving personal hygiene

16. What are pond scum?

(a) algae

(b) protozoa

(c) fungi

(d) bacteria

► (a) algae

17. A plant disease called citrus canker is caused by a _________ .

(a) Virus

(b) Protozoa

(c) Bacteria

(d) Fungi

► (c) Bacteria

18. Bacteriophage is a :

(a) fungi

(b) protozoa

(c) virus

(d) bacteria

► (c) virus

19. Which of the following statements describes bacteriophage correctly?

(a) It is a bacterium which causes diseases in plants.

(b) It is a type of virus which attacks bacteria.

(c) It is a bacterium which kills viruses.

(d) It can multiply inside both living and non-living cells.

► (b) It is a type of virus which attacks bacteria.

20. Which of the following is the smallest microorganism?

(a) Algae

(b) Bacterium

(c) Protozoan

(d) Virus

► (d) Virus

21. Which of the following enzymes is secreted by bacteria that can digest cellulose?

(a) Amylase

(b) Cellulase

(c) Lipase

(d) Protease

► (b) Cellulase

22. Which of the following microorganism lives alone:

(a) Amoeba

(b) All Bacteria

(c) Fungi

(d) All Cyanobacteria

► (a) Amoeba

23. Which two words are synonyms?

(a) Microorganism and pathogen

(b) Microorganism and microbe

(c) Microbe and aerobe

(d) Microbe and anaerobe

► (b) Microorganism and microbe

24. Curd formations needs :

(a) citric acid bacterium

(b) acetic acid bacterium

(c) lactic acid bacterium

(d) all the above

► (c) lactic acid bacterium

25. TMV causes disease in :

(a) tobacco plant

(b) human infants

(c) timber plants

(d) none of the above

► (a) tobacco plant

26. Scientist who discovered the fermentation

(a) Alexander Fleming

(b) Louis Pasteur

(c) John Mendal

(d) Charles Darwin

► (b) Louis Pasteur

Important Questions Class 8 Science Chapter 2 – With Solutions

Question 1. Pathogenic microorganisms present in host cells are killed by ____.

• antibiotics
• antibodies
• vaccines
• pain killers

Answer 1: The correct option is A- Antibiotics.

Explanation:

Antibiotics are those substances that may inhibit or kill the growth of different microbes. Antibiotics are antimicrobial drugs from other organisms (such as moulds, fungus and some soil bacteria) to combat harmful microorganisms. The consumption of these antibiotics kills the microorganisms causing infection in host bodies. The definition of a pathogenic organism is the organism capable of causing disease in its host. A human pathogen has the capability of causing illness in humans. Common examples of various pathogenic organisms include specific strains of bacteria like Salmonella, Listeria and E. coli, and other viruses such as Cryptosporidium. An antibiotic is a chemical substance that inhibits the growth of these harmful bacteria. They hinder the bacteria’s reproductive cycle inside the host’s body.

Question 2. How do vaccines work?

Answer 2:

Vaccines are treatments that improve your immunity to a certain disease. Vaccines contain dead or weakened but alive microorganisms of a particular disease. When a vaccine containing dead or alive microorganisms is introduced into a healthy body, orally (by mouth) or by injection, that person’s body triggers an immune response. The immune system of the person, in turn, responds by producing some substances called antibodies in its blood to protect against the pathogens introduced. These antibodies kill the ‘live’ disease-causing microorganisms present in the vaccine. Some of the antibodies remain in the person’s blood for a very long time and fight against the same microorganism and kill them if they enter the body naturally later. So, due to antibodies in the blood, a person remains protected from that disease. With a vaccine, the immune system can safely learn to recognize them as hostile invaders, produce antibodies, and remember them for the future.

Thus, a vaccine develops immunity from a disease.

Question 3. Write a paragraph on the harms caused by microorganisms.

Answer 3:

Microorganisms are causative agents in many infectious diseases. Therefore, microbes are termed pathogens. Microorganisms are very minute organisms that are invisible to the human eye. Microorganisms are so tiny that they can be seen only under a microscope. These include many organisms such as bacteria, viruses, fungi, algae, protozoa, etc. Some microbes prove beneficial; however, most microorganisms can be very harmful to us. They cause many diseases in humans, plants and animals that prove to be fatal.

Harmful effects of microorganisms are:

• Some microorganisms are pathogens which cause diseases to humans, animals and plants.
• Bacteria and fungi cause food spoilage and make them unfit for eating. Consumption of such food causes food poisoning. 
• Human diseases like the common cold, tuberculosis, measles, chicken pox, polio, cholera, typhoid, hepatitis B, malaria, etc., are caused by microorganisms. 
• Some serious diseases like anthrax are also caused in animals by microbes. 
• Microbes also cause diseases in plants like blights in potatoes, sugarcanes, oranges etc. Some viruses can affect cattle by causing foot and mouth disease. 
• They are also responsible for reducing crop yield, causing loss to farmers.
• Microbes also spoil clothing and leather products. They reduce the lifespan and the quality of the product.

Question 4. What are the major groups of microorganisms?

Answer 4:

Microorganisms are very minute organisms that are invisible to the human eye. Microorganisms are so minute that they can only be seen under the microscope. Microorganisms include bacteria, fungi, archaea or protists. Microorganisms differ in size and structure, habitat, metabolism, and many other characteristics. Most bacteria are harmless or helpful, but some are pathogens, causing disease in humans and other animals.

There are five major groups of microorganisms. They are enlisted as

• Bacteria:

It is a single-celled organism.

They can be spiral, rod-shaped, spherical-shaped, or comma-shaped.

It causes diseases like cholera, tetanus and tuberculosis.

• Fungi:

Fungi are usually multicellular organisms that cause several diseases.

Symptoms depend on the area affected

The moulds formed on bread are a specific type of fungi.

• Protozoa:

Protozoa can either be multicellular or unicellular.

Amoeba and Plasmodium are a few examples of protozoa.

They can be harmful to humans as well as different other organisms.

• Virus:

Viruses are disease-causing microorganisms that can only divide inside a host organism/cell. 

They remain inactive outside the cell.

It can affect plants, animals as well as humans. 

HIV in humans and TMV virus occurring in plants are some examples of viruses.

• Algae:

These are the only microorganisms that are multicellular. 

Algae have photosynthetic pigments.

They are also known as precursors of plants.

Spirogyra and Chlamydomonas are some examples of algae.

Question 5. The bread or idli dough rises because of ______.

• heat
• grinding
• growth of yeast cells
• kneading

Answer 5: The correct option is C- growth of yeast cells

Explanation:

Yeast can be utilised as a leavening agent in bread and idli making. The yeast consumes the sugar in the dough and burps carbon dioxide gas and ethanol. This gas is trapped inside the bread dough due to gluten present in it, thus making the dough rise. The alcohol also gets evaporated in the baking process. While bread-making, the dough is left in a warm place. During fermentation, carbon dioxide gas is produced and gets trapped in tiny pockets of air within the dough. This makes the dough rise. If you let the dough rise for too long, the finished bread’s taste and texture suffer. Due to different yeast cell development, the dough of bread or idli rises. If there is lots of food present around to take advantage of the food, the yeast cells reproduce in great numbers. They normally develop a tiny bud from one edge of themselves when they reproduce. Then a small nucleus is placed and pinched off to make a smaller new yeast cell. The leavening agent or yeast converts sugars in the dough to carbon dioxide and derives energy from this reaction. Due to this, yeast cells grow, and the dough also expands. Hence, the bread and idli develop a soft and spongy texture. 

Question 6. Explain the nitrogen cycle.

Answer 6:

The nitrogen cycle is the continuous process of exchanging nitrogen between organisms and the environment. Nitrogen is an essential nutrient needed to make amino acids and other important organic compounds. Still, most organisms cannot use free nitrogen, which is abundant as a gas in the atmosphere. This is a biogeochemical process through which nitrogen is converted into many forms, consecutively passing from the atmosphere to the soil to the organism and back into the atmosphere. Nitrogen is an important plant nutrient. However, plants and animals cannot directly use the plentiful nitrogen in the atmosphere. Nitrogen nitrification, nitrogen fixation, decay, and putrefying are among the mechanisms that pass from the ambience to the soil to the organism and then return to the atmosphere. Nitrogen gas exists in both organic as well as inorganic forms. 

Organic nitrogen primarily exists in living organisms, and it gets passed through the food chain by consuming other living organisms. 

While the inorganic forms of nitrogen are present in abundance in our atmosphere. This inorganic form of nitrogen is available for plants through symbiotic bacteria, which converts the inert nitrogen into a more usable form – such as nitrates and nitrites. Nitrogen will undergo a wide range of transformations to maintain a good ecosystem balance. This process extends to diverse biomes. The marine nitrogen cycle is known to be one of the most intricate biogeochemical cycles.

The nitrogen cycle is about the movement of nitrogen occurring between various elements on Earth (like air, soil, living organisms etc.). The amount of the element nitrogen in the atmosphere remains constant.

• The atmosphere contains approximately 78% nitrogen.
• Atmospheric nitrogen gets fixed into the soil.
• N2 fixing microbes facilitate the conversion of atmospheric N2 into nitrogen compounds like NH3.
• The plants utilise nitrogen from soil through their roots.
• Animals utilise nitrogen, feeding on plants.
• When plants & animals die, nitrogenous wastes are returned to the soil.
• Decomposers convert some parts to nitrogen compounds to be used by plants.
• Denitrifying bacteria convert into atmospheric N2.

Question 7. What are antibiotics? What precautions must be taken while taking antibiotics?

Answer 7:

Antibiotics are medicines produced by certain microorganisms which kill or stop the growth of microorganisms in our body. These are very effective in preventing the effects of microorganisms. Antibiotics are made from bacteria and fungi. Antibiotics treat various human and animal diseases as they target bacteria and viruses. They have significantly enhanced our ability to treat severe diseases like plague, whooping cough, and leprosy. Examples of general antibiotics are streptomycin, tetracycline, erythromycin etc.

Precautions to be taken while taking antibiotics:

• Antibiotics should only be taken under the guidance of a skilled physician.
• Antibiotics must only be taken when needed and in an adequate amount. Otherwise, they may be harmful and will become less effective in future.
• The antibiotic course should be finished according to the doctor’s instructions.
• Antibiotics must be administered in the correct dosage and at the appropriate time.
• Antibiotics that are given in the wrong dose become useless.
• Excessive medication usage might also harm the beneficial bacteria in our bodies.

Read more about Science Class 8 Chapter 2 important questions on Extramarks.

Question 8. Write ten lines on the usefulness of microorganisms in our lives.

Answer 8:

Microorganisms are very minute organisms that are invisible to the naked eye. However, these microbes are vital to plants and the environment. Here are some uses of microorganisms in our daily life.

• Some microorganisms are used as a probiotic (live bacteria and yeasts that are good for the digestive system and maintain the good health of the host). They are called ‘good’ or ‘useful’ bacteria.
• In pulse plants’ roots, rhizobium fixes nitrogen from the air and supplies nitrogen compounds to the pulse plants. It also helps to make the soil more fertile.
• Microorganisms are used in winemaking, baking, pickling, and other food-making processes.
• Alcoholic fermentation by yeast is widely used for the commercial preparation of wine and bread. Yeast makes idli, bhaturas, bread, pastries, and cakes.

• Microbes are used to reduce pollution. For example, decomposers like bacteria and fungi break down dead bodies and excreta for forming inorganic compounds, which plants can easily absorb.
• Microbes also play a crucial role in the preparation of medicines. Antibiotics are chemicals produced by microorganisms to kill bacteria. Penicillin is an antibiotic made from penicillium.
• Bacteria in our intestine help in proper digestion and release vitamin B, absorbed by the intestine. They induce immunity in our bodies.
• Many vaccines are prepared from microorganisms. These vaccines are usually given to children to protect them from the disease.
• Certain microbes are used in the biological treatment of sewage and industrial effluents.
• Lactobacillus is used in dairy industries for the setting of curd and cheese making. Microorganisms carry out the processing and ageing of cheese.

Question 9. What measures can be taken to prevent the spread of communicable diseases?

Answer 9:

Infectious diseases are communicable diseases that can spread from one person to another. Chickenpox, mumps, influenza etc., are a few examples of communicable diseases.

Precautions to prevent the spreading of communicable diseases:

• Wash your hands often: This is mainly important before and after preparing food, eating, and after the toilet is used.
• Get vaccinated: Immunisation can have a drastic reduction in your chances of contracting many diseases. Keep the recommended vaccinations up-to-date.
• Use of antibiotics sensibly: Take antibiotics only when you are prescribed. Unless directed, or unless you are allergic to these antibiotics, take all prescribed doses of your antibiotic, even though you begin to feel better before you have finished the medication.
• Stay at home if you observe signs and symptoms of an infection: Don’t go to work or class if you’re vomiting, have diarrhoea or are running a fever.
• Be smart in food preparation: Keep counters, and kitchen surfaces clean when preparing meals. In addition, promptly refrigerate your food leftovers. Never let the cooked foods remain at room temperature for a long period.
• Practice safer sex: Use condoms. Get tested for various sexually transmitted diseases (STDs), and have your partner get tested— or abstain altogether.
• Don’t share personal items: Use your toothbrush, comb or razor blade. Avoid sharing drinking glasses or dining utensils.
• Travel wisely: Avoid going to public places or events when ill.

Benefits of Solving Important Questions Class 8 Science Chapter 2

Science is a broad subject with multiple theories and concepts. All of this makes it difficult for students to understand and remember. Students are encouraged to go through Extramarks question bank of Important Questions Class 8 Science Chapter 2. Students can gather confidence by answering the important questions and going over their provided solutions. The Important Questions Class 8 Science Chapter 2  provides a strong foundation of basic concepts among students. These step-wise solutions will help you to attain perfection on the concepts involved in the chapter ‘Microorganisms: Friend and Foe’. 

Mentioned below are some benefits of solving Important Questions Class 8 Science Chapter 2:

• These solutions will help students to save time while preparing for their upcoming examination and cover the entire chapter as well as revise crucial concepts covered in the chapter.
• Important Questions Class 8 Science Chapter 2 covers the majority of concepts of the entire chapter-Introduction to microorganisms, their habitats, classes of microorganisms like bacteria, fungi, protozoans and viruses, mode of their reproduction, use of microorganisms, harmful microorganisms, pathogens, soil microorganisms, nitrogen fixation by bacteria.
• Students can entirely rely upon these important questions as these solutions are prepared following all the guidelines laid by CBSE.
• Class 8 Science Chapter 2 important questions are compiled by the experts at Extramarks who have experience in teaching Biology and Science related subjects for several years.

Extramarks provides students from Class 1 to Class 12 with comprehensive learning solutions. Our website has abundant study materials and resources, along with important questions and solutions. Students can easily click on the links given below to get access to important questions Class 8 Science Chapter 2 along with some of these other resources:

MCQ Questions for Class 8 Science: Ch 1 Crop Production and Management

1. Weedicides are used to destroy:

(a) insects

(b) weeds

(c) pests

(d) none of these

► (b) weeds

2. Cutting mature crop manually or by a machine is called:

(a) Irrigating

(b) Harvesting

(c) Breeding

(d) Weeding

► (b) Harvesting

3. Grains are separated from stalks by a process called________

(a) Harvesting

(b) Threshing

(c) Weeding

(d) Winnowing

► (b) Threshing

4. The medium of growth for plants is :

(a) Cell

(b) Soil

(c) Water

(d) Air

► (b) Soil

5. Breeding, rearing and management animals for human use is :

(a) Aniculture

(b) Animal husbandry

(c) Animal culture

(d) None of these

► (b) Animal husbandry

6. The rearing of honey bees on large scale is called:

(a) sericulture

(b) tissue culture

(c) pisciculture

(d) apiculture

► (d) apiculture

7. Any plant cultivated at a large stretch of land is called :

(a) Crop

(b) Weed

(c) Cereal

(d) Fibre

► (a) Crop

8. Watering the crops is called:

(a) sowing

(b) manuring

(c) tilling

(d) irrigation

► (d) irrigation

9. Crop plants may be attacked by pests which affect the crop production. Fungi are such type of pests which cause diseases like

(a) Smut of wheat

(b) Citrus canker

(c) Blight of potato

(d) Both (a) and (c)

► (d) Both (a) and (c)

10. The manure prepared from green plants is :

(a) FYM

(b) Compost

(c) Green manure

(d) all the above

► (c) Green manure

11. Which of the following tools would a farmer use to remove weeds from the field?

(a) Hoe

(b) Axe

(c) Plough

(d) Cultivator

► (a) Hoe

12. Take a beaker and fill half of it with water. Put some wheat seeds in it, stir it and wait for some time. Which of the following holds true regarding the observation and inference of this experiment?

(a) Healthy seeds being lighter float on the surface of water.

(b) Damaged seeds being lighter float on the surface of water.

(c) Some healthy seeds and some damaged seeds float on the surface of water.

(d) Damaged seeds being heavier settle down at the bottom.

► (b) Damaged seeds being lighter float on the surface of water.

13. Combines are used for:

(a) sowing of seeds

(b) harvesting the crops

(c) threshing

(d) harvesting and threshing both

► (d) harvesting and threshing both

14. Peas are rich in:

(a) vitamins

(b) carbohydrates

(c) proteins

(d) fats

► (c) proteins

15. Improper use of fertilizers can cause:

(a) soil alkalinity & soil acidity

(b) soil acidity only

(c) soil acidity and soil erosion

(d) soil erosion

► (a) soil alkalinity & soil acidity

16. The system of irrigation wherein water is supplied drop by drop near the roots of plants, is called

(a) Sprinkler system

(b) Pulley system

(c) Lever system

(d) Drip system

► (d) Drip system

17. Wheat and gram belong to

(a) Rabi crops

(b) Kharif crops

(c) Both of these

(d) None of these

► (a) Rabi crops

18. The agricultural implement used for removing weeds and for loosening soil is :

(a) Combine

(b) Drill

(c) Hoe

(d) Cultivator

► (c) Hoe

19. The cutting and gathering of crop after it is matured is called X. After this, grains are separated from the crop by a process called Y. Z is the process of separating the hay and chaff from the grains. Which of the following statements is/are correct regarding X, Y and Z?

(a) Z is done with the help of wind in which grains along with husk is allowed to fall from a height.

(b) X is done mechanically by combine and manually by plough and harrow.

(c) X is the process known as threshing whereas Y is the process known as winnowing.

(d) Both (a) and (b)

► (a) Z is done with the help of wind in which grains along with husk is allowed to fall from a height.

20. Examples of kharif crops are

(a) Wheat and maize

(b) Gram and maize

(c) Paddy and maize

(d) All of these

► (c) Paddy and maize

21. Seed drill is used to

(a) sow the seeds

(b) remove the weeds

(c) remove the pest

(d) mix manure in the soil

► (a) sow the seeds

22. Cereals provide us mainly :

(a) carbohydrates

(b) proteins

(c) fats

(d) fibre

► (a) carbohydrates

23. Food provides _________ and materials required for the growth and maintenance of our body

(a) energy

(b) nutrition

(c) power

(d) none of the above

► (a) energy

24. Coconut provides us mainly :

(a) fat

(b) milk

(c) protein   

(d) carbohydrate

► (c) protein   

Crop Production and Management Class 8 Extra Questions Short Answer Type

Question 1.
What is a crop?
Answer:
Crop is the term used to describe a plant that is grown in a field on a large scale. For example, cereal crops, wheat crops.

Question 2.
What do you mean by produce?
Answer:
The products obtained from the crops are called produce.

Question 3.
What do you mean by the term agricultural practice?
Answer:
Agricultural practices are those practices which involve the necessary steps to be taken during production of crops.

Question 4.
Explain the term levelling.
Answer:
Levelling is the process of breaking down the larger lumps of soil, and then levelling them by using a leveller.

Question 5.
What are the advantages of levelling?
Answer:
Following are the advantages of levelling:

• Levelling helps to prevent soil erosion caused by wind or air.
• It helps in sowing the seeds uniformly, and thus helps the plants to grow uniformly too.
• It helps in proper irrigation by allowing the water to get distributed uniformly throughout the soil.

Question 6.
What is a plough?
Answer:
A plough is an equipment for ploughing. It is mainly made of a wooden shaft called a plough-shaft, attached to a triangular iron blade called ploughshare.

Question 7.
What is a cultivator?
Answer:
Cultivator is a farm implement used for stirring and pulverizing the soil for planting crops.

Question 8.
Explain the term transplantation.
Answer:
Some of the crops are first grown in the nurseries and then transferred to the main field. This process is known as transplantation.

Question 9.
What are the advantages of manure?
Answer:
Following are some advantages of manure:

• It enhances water-holding capacity of soil.
• It improves soil quality.
• It promotes the growth of soil friendly microbes.
• It is renewable, biodegradable and eco-friendly.

Question 10.
What are weedicides? Give some examples.
Answer:
Weedicides are the chemicals that are used to remove weeds. Some commonly used weedicides are 2, 4-D and metachlor.

Crop Production and Management Class 8 Extra Questions Long Answer Type

Question 1.
What do you mean by the term crop? Explain briefly the types of crops.
Answer:
Crop is the term used to describe a plant that is grown in a field on a large scale. For example, cereal crops, pulses and fruit crops. The crops grown in India can be classified as kharif and rabi.

Kharif crops are sown in the rainy season by June/July and are harvested by September/October. Thus they are also known as summer season crops. For example, rice, maize, etc.

Rabi crops are sown in the winter season in October or November and are harvested by March/April. Thus, they are also called winter season crops. For example, mustard, wheat, potato, etc.

Question 2.
What is ploughing or tilling? State its advantages.
Answer:
The process of loosening and turning of the soil is called tilling or ploughing. This is done by using a plough. Ploughs are made of wood or iron. Following are the advantages of ploughing or tilling:

• Ploughing loosens the soil and makes it aerated.
• It helps in mixing organic matter with the soil uniformly.
• It initiates the growth of natural agents and microorganisms and thus, keeps the soil fertile.
• It increases the water holding capacity of soil.
• It helps in easy penetration of root into the soil.

Question 3.
Define the term agricultural practices and also state the important steps taken during crop production.
Answer:
Agricultural practices are those practices which involves the necessary steps to be taken during production of crops. There are number of steps of crop production which are to be done very carefully to ensure that crops get produced timely. Some of the most important steps taken during crop production are as under:

• Soil preparation
• Sowing
• Adding manure and fertilisers
• Irrigation
• Weeding
• Harvesting
• Threshing and winnowing
• Storage of grains

Question 4.
What is irrigation? Name the two main methods of irrigation and define them briefly.
Answer:
The artificial method of watering the plants for assisting in the growth of the plants is called irrigation. The two main methods of irrigation are:
(i) Traditional method: The traditional method of irrigation is very less expensive and they often lead to wastage of water. Traditional method of irrigation involves chain pump, dhekli, moat (the pulley system) and rahat (lever system).

(ii) Modern method: Modern methods of irrigation are more inclined towards the use of diesel, bio¬gas, solar energy and electricity for lifting water.
The two most important modern system of irrigation are:

• Sprinkler irrigation system
• Drip irrigation system

Question 5.
What do you mean by weeding? Why the process of weeding necessary? Name the methods applied for weeding.
Answer:
The undesirable plants that grow among the crops are called weeds. The process of removing these weeds is known as weeding. Weeds compete with the crop plants for nutrients and space. They grow much rapidly than the crop plant. So weeding is necessary.

Methods applied for weeding are as follows:
(i) Manual method: Manual method of removing weeds is the most time consuming method. In this system weeds are controlled by hand pulling, digging, shallow tillage, etc., by using certain implements like khurpi, hoe, etc.

(ii) Chemical method: In this method chemicals called, weedicides are used to remove weeds. For example, metachlor and 2, 4-D.

(iii) Biological control method: This method is the most commonly used method of weed control. It involves the use of some specific insects that destroy the growth of some specific weeds. For example, leafy spurge, a weed, is controlled by using flea beetles.

Question 6.
Write short note on the terms:
(i) Storage
(ii) Harvesting
Answer:
(i) Storage: Storage of produce is an important task. If the crop grains are to be kept for longer time, they should be safe from moisture, insects, rats and microorganisms. Before storing, the grains are properly dried in the sun to reduce the moisture in them. This prevents the attack by insect pests, bacteria and fungi. Grains are stored by farmers in jute bags or metallic bins. However, large scale storage of grains is done in silos and granaries to protect them from pests like rats and insects.

(ii) Harvesting: After maturation of crop, harvesting is an important task. In harvesting, crops are pulled out or cut close to the ground. It usually takes 3 to 4 months for a cereal crop to mature. Harvesting in our country is either done manually by sickle or by machine called harvester.

Crop Production and Management Class 8 Extra Questions HOTS

Question 1.
Why the depth at which seeds are planted is important?
Answer:
If the seed is planted too deep then it will not get enough sunlight to germinate. If the seed is planted too shallow then it will not get enough soil to support germination. The depth for sowing seed also depends upon the seed size.

Question 2.
Why sowing seeds with seed drill is better than broadcasting?
Answer:
Seed drill sows the seeds uniformly at proper distances and depths, whereas broadcasting of seeds scatter them non-uniformly on the ground surface which are susceptible to be picked up by birds.

Question 3.
How can nitrogen be replenished in soil naturally?
Answer:
Through crop rotation with a leguminous crop the nitrogen can be replenished in soil naturally. The leguminous plants, like peas, beans, soybeans, peanuts, etc., have nitrogen-fixing bacteria in their root nodules. The nitrogen-fixing bacteria, viz., Rhizobium, fixes atmospheric nitrogen (N₂) into ammonium (NH₄₊) which is used by the plants.

Question 4.
Why is it advisable to wash fruits and vegetables before using them?
Answer:
Fruits and vegetables may contain many pesticides, used during the crop production practices, on them along with other germs and dust.

Question 5.
What is biological control of pest? How is it beneficial?
Answer:
Method of controlling pests including insects, mites, weeds, etc., with the help of other living organisms are known as biological control of pest. The controlling agents are very much particular of their host pest. For example, lady bugs controls aphids, mites, scale insects, etc., which harm the crops. A wasp eats up bollworms or other caterpillars on cotton plant.
Benefits of biocontrol agents are:

• Less costly
• Give protection to the crop throughout the crop period
• Eco-friendly
• Harmless to human beings and beneficial to flora and fauna

MCQ Questions for Class 8 Maths: Ch 16 Playing with Numbers

1. The generalised form of the number 33 is

(a) 10 × 3 + 3

(b) 10 × 3

(c) 3 + 3

(d) 3 × 3 + 3

► (a) 10 × 3 + 3

2. Which of the following statements is false?

(a) If a number is divisible by 8, it must be divisible by 4.

(b) If a number is divisible by both 9 and 10, it is divisible by 90.

(c) The sum of two consecutive odd numbers is always divisible by 4.

(d) If a number is not divisible by both 3 and 4, it is divisible by 12.

► (d) If a number is not divisible by both 3 and 4, it is divisible by 12.

3. Which of the given numbers is composite?

(a) 137

(b) 147

(c) 157

(d) 167

► (b) 147

4. If the division N ÷ 5 leaves a remainder of 0, what might be the one’s digit of N?

(a) 5

(b) Either 5 or 0

(c) 2

(d) 7

► (b) Either 5 or 0

5. Write in generalised form: 25

(a) 10 × 5 + 2

(b) 10 × 5 + 3

(c) 10 × 2 + 5

(d) 10 × 3 + 5

► (c) 10 × 2 + 5

6. Which of these numbers is divisible by 6?

(a) 5782

(b) 2666

(c) 6053

(d) 8964

► (d) 8964

7. By which of the following number 9042 is not divisible? 2, 3, 6, and 9

(a) 2

(b) 3

(c) 9

(d) 6

► (c) 9

8. Write in generalised form: 85

(a) 10 × 5 + 8

(b) 10 × 8 + 5

(c) 10 × 5 + 3

(d) 10 × 3 + 5

► (b) 10 × 8 + 5

9. What value should be given to * so that the number 653∗47 is divisible by 11?

(a) 1

(b) 6

(c) 2

(d) 9

► (a) 1

10. N is a 5-digit number divisible by 5. If N is bigger than 10000 and smaller than 10010, what is the value of N?

(a) 10000

(b) 10010

(c) 10005

(d) 10001

► (c) 10005

11. When is a number always divisible by 90?

(a) If it is divisible by both 2 and 45.

(b) If it is not divisible by both 5 and 18.

(c) If it is not divisible by both 9 and 10.

(d) If it is divisible by 3 and 20.

► (a) If it is divisible by both 2 and 45.

12. By which of the following numbers is 477 not divisible?

(a) 3

(b) 7

(c) 53

(d) 9

► (b) 7

13. Write in the usual form: 10×5 + 6

(a) 65

(b) 54

(c) 56

(d) 25

► (c) 56

14. Identify the missing digit in the number 234,4_6, if the number is divisible by 4.

(a) 2

(b) 6

(c) 4

(d) 5

► (d) 5

15. Write in the usual form: 100 × 7 + 10 × 1 + 8

(a) 871

(b) 718

(c) 178

(d) 781

► (b) 718

16. Which of the following is not prime?

(a) 107

(b) 127

(c) 153

(d) 197

► (c) 153

17. By which of the following number 168 is divisible?

(a) 5

(b) 10

(c) 9

(d) 2

► (d) 2

18. 32 + m is a prime number. What is the least value of ‘m’?

(a) 3                                    

(b) 5    

(c) 6                    

(d) 4

► (b) 5    

19. Which of the following is divisible by 12?

(a) 284382                         

(b) 624876         

(c) 926248         

(d) 746174   

► (b) 624876         

20. If a number is divisible by 9, it is also divisible by which number?

(a) 3

(b) 6

(c) 2

(d) 4

► (a) 3

Playing with Numbers Class 8 Extra important Questions Very Short Answer Type

Question 1.
Write the following numbers in generalised form.
(a) ab
(b) 85
(c) 132
(d) 1000
Solution:
(a) ab = 10 × a + 1 × b = 10a + b
(b) 85 = 10 × 8 + 1 × 5 = 10 × 8 + 5
(c) 132 = 100 × 1 + 10 × 3 + 1 × 2 = 100 × 1 + 10 × 3 + 2
(d) 1000 = 1000 × 1

Question 2.
Write the following in usual form.
(a) 3 × 100 + 0 × 10 + 6
(b) 5 × 1000 + 3 × 100 + 2 × 10 + 1
Solution:
(a) 3 × 100 + 0 × 10 + 6 = 300 + 0 + 6 = 306
(b) 5 × 1000 + 3 × 100 + 2 × 10 + 1 = 5000 + 300 + 20 + 1 = 5321

Question 3.
Which of the following numbers are divisible by 3?
(i) 106
(ii) 726
(iii) 915
(iv) 1008
Solution:
(i) Sum of the digits of 106 = 1 + 0 + 6 = 7 which is not divisible by 3.
Hence 106 is not divisible by 3.
(ii) Sum of the digits of 726 = 7 + 2 + 6 = 15 which is divisible by 3.
Hence 726 is divisible by 3.
(iii) Sum of the digits of 915 = 9 + 1 + 5 = 15 which is divisible by 3.
Hence 915 is divisible by 3.
(iv) Sum of the digits of 1008 = 1 + 0 + 0 + 8 = 9 which is divisible by 3.
Hence 1008 is divisible by 3.

Question 4.
Prove that the sum of the given numbers and the numbers obtained by reversing their digits is divisible by 11.
(a) 89
(b) ab
(c) 69
(d) 54
Solution:
(a) Given number = 89
Number obtained by reversing the order of digits = 98
Sum = 89 + 98 = 187 ÷ 11 = 17
Hence, the required number is 11.

(b) Given number = ab = 10a + b
Number obtained by reversing the digits = 10b + a
Sum = (10a + b) + (10b + a)
= 10a + b + 10b + a
= 11a + 11b
= 11(a + b) ÷ 11
= a + b

(c) Given number = 69
Number obtained by reversing the digits = 96
Sum = 69 + 96 = 165 ÷ 11 = 15
Hence, the required number is 11.

(d) Given number = 54
Number obtained by reversing the digits = 45
Sum = 54 + 45 = 99 ÷ 11 = 9
Hence, the required number is 11.

Question 5.
Prove that the difference of the given numbers and the numbers obtained by reversing their digits is divisible by 9.
(i) 59
(ii) xy
(iii) xyz
(iv) 203
Solution:
(i) Given number = 59
Number obtained by reversing the digits = 95
Difference = 95 – 59 = 36 ÷ 9 = 4
Hence, the required number is 9.

(ii) Given number = xy = 10x + y
Number obtained by reversing the digits = 10y + x
Difference = (10x + y) – (10y + x)
= 10x + y – 10y – x
= 9x – 9y
= 9(x – y) ÷ 9
= x – y
Hence, the required number is 9.

(iii) Given number = xyz = 100x + 10y + z
Number obtained by reversing the digits = 100z + 10y + x
Difference = (100x + 10y + z) – (100z + 10y + x)
= 100x + 10y + z – 100z – 10y – x
= 99x – 99z
= 99(x – z)
= 99(x – 2) ÷ 9
= 11 (x – z)
Hence, the required number is 9.

(iv) Given number = 203
Number obtained by reversing the digits = 302
Difference = 302 – 203 = 99 ÷ 9 = 11
Hence, the required number is 9.

Question 6.
If a, b, c are three digits of a three-digit number, prove that abc + cab + bca is a multiple of 37.
Solution:
We have abc + cab + bca
abc = 100a + 10b + c
cab = 100c + 10a + b
bca = 100b + 10c + a
Adding abc + cab + bca = 111a +111b + 111c
= 111 (a + b+ c)
= 37 × 3 (a + b + c) which is a multiple of 37.
Hence proved.

Playing with Numbers Class 8 Extra Questions Short Answer Type

Question 7.
Complete the magic square given below so that the sum of the numbers in each row or in each column or along each diagonal is 15.

Solution:
(i) A = 15 – (8 + 1) = 15 – 9 = 6
(ii) F = 15 – (8 + 5) = 15 – 13 = 2
(iii) C = 15 – (A + F) = 15 – (6 + 2) = 15 – 8 = 7
(iv) E = 15 – (1 + 5) = 15 – 6 = 9
(v) D = 15 – (E + F) = 15 – (9 + 2) = 15 – 11 = 4
(vi) B = 15 – (8 + 4) = 15 – 12 = 3
Hence the required square is

Question 8.
Find the values of P and Q from the given addition problem

Solution:
Here, 3 + Q = 7
⇒ Q = 7 – 3 = 4
Now taking second column, we get
4 + 7 = 11 i.e. 1 is carried over to third column
⇒ 1 + P + 2 = 9
⇒ 3 + P = 9
P = 9 – 3 = 6
Hence the value of P = 6 and Q = 4

Question 9.
Find the values of p, q and r in the following multiplication problem.

Solution:
6 × 4 = 24, Here 2 is carried over second column
⇒ 6 × p + 2 – 3 × 10 = 2 [∵ 21 – 3 × 6 = 3]
⇒ 6p – 30 = 0
⇒ p = 5
Now the multiplication problem becomes,

Here 2 + r = 4
⇒ r = 2
q × 354 = 1062
⇒ q = 3
Hence, p = 5, q = 3, r = 2

Question 10.
Observe the following patterns:
1 × 9 – 1 = 8
21 × 9 – 1 = 188
321 × 9 – 1 = 2888
4321 × 9 – 1 = 38888
Find the value of 87654321 × 9 – 1
Solution:
From the pattern, we observe that there are as many eights in the result as the first digit from the right which is to be multiplied by 9 and reduced by 1.
87654321 × 9 – 1 = 788888888

Playing with Numbers Class 8 Extra Questions High Order Thinking Skills (HOTS) Type

Question 11.
Complete the cross number puzzle with the given column.


Solution:

Hence the complete square is

Question 12.
The product of two 2-digit numbers is 1431. The product of their tens digits is 10 and the product of their units digits is 21. Find the numbers. Solution:
Let the required two 2-digit numbers be 10a + b and 10p + q as per the condition, we have
a × p = 10 and b × q = 21
a = 2 and p = 5 or a = 5 and p = 2
Similarly b × q = 21
b = 3 and q = 7 or b = 7 and q = 3
10p + q = 57 or 10p + q = 53
and 10a + b = 23 or 10a + b = 27
Since the units digit of product 1431 is 1.
Numbers are 57 and 23 or 53 and 27.
Now 57 × 23 = 1311 and 53 × 27 = 1431 which is given.
Hence, the required numbers are 53 and 27.

MCQ Questions for Class 8 Maths: Ch 15 Introduction to graphs

1. Find the distance covered in 6 seconds. 

(a) 30 m

(b) 35 m

(c) 25 m

(d) none of these

► (a) 30 m

2. Find the distance covered in 5 seconds.

(a) 25 m

(b) 10 m

(c) 20 m

(d) none of these

► (a) 25 m

3. Find the coordinates of the point E from the graph.

(a) (1, -1)

(b) (-4, 5)

(c) (0, -4)

(d) None of these

► (a) (1, -1)

4. Find the coordinates of the point F from the graph.

(a) (-4, 5)

(b) (-2, -1)

(c) (0, -4)

(d) None of these

► (b) (-2, -1)

5. Find the distance covered in 2 seconds.

(a) 15 m

(b) 20 m

(c) 25 m

(d) 10 m

► (d) 10 m

6. On which axis does the point (0, 5) lie?

(a) origin

(b) x-axis

(c) y-axis

(d) None of these

► (c) y-axis

7. Which of the points given is a point on the X-axis?

(a) (5,0)

(b) (0,5)

(c) (5,3)

(d) (3,5)

► (a) (5,0)

8. Find the coordinates of the point C from the graph.

(a) (1, 3)

(b) (-4, 5)

(c) (0, -4)

(d) None of these

► (a) (1, 3)

9. In which quadrant does the point Q (-2, -6) lie?

(a) I

(b) II

(c) IV

(d) III

► (d) III

10. On which axis does the point (-1, 0) lie? 

(a) x-axis

(b) origin

(c) y-axis

(d) None of these

► (a) x-axis

11. The line graph shows the yearly sales figure for a manufacturing company. From the graph, what were the sales in 2006?

(a) Rs 8 millions

(b) Rs 4 millions

(c) Rs 3 millions

(d) Rs 5 millions

► (a) Rs 8 millions

12. The line graph shows the yearly sales figure for a manufacturing company. From the graph, what were the sales in 2004?

(a) Rs 5 millions

(b) Rs 3 millions

(c) Rs 4 millions

(d) Rs 6 millions

► (d) Rs 6 millions

13. Which of the following statements is true?

(a) The X-axis is a vertical line.

(b) The Y-axis is a horizontal line.

(c) The scale on both the axes must be the same in a Cartesian plane.

(d) The point of intersection between the X-axis and Y-axis is called the origin.

► (d) The point of intersection between the X-axis and Y-axis is called the origin.

14. Find the time taken by a body to cover 5 metres.

(a) 3 seconds

(b) 4 seconds

(c) 5 seconds

(d) 1 second

► (d) 1 second

15. Find the coordinates of the point A from the graph. 

(a) (-4, 5)

(b) (-4, 0)

(c) (0, -4)

(d) none of these

► (b) (-4, 0)

16. Find the distance covered in 7 seconds.

(a) 30 m

(b) 25 m

(c) 35 m

(d) 20 m

► (c) 35 m

MCQ Questions for Class 8 Maths: Ch 14 Factorisation

 

MCQ Questions for Class 8 Maths: Ch 14 Factorisation

1. The common factor of a² m⁴ and a⁴m² is
(a) a⁴m⁴
(b) a²m²
(c) a²m⁴
(d) a⁴m²

► (b) a²m²

2. Divide as directed: 26xy (x + 5) (y – 4) ÷ 13x (y – 4)
(a) 2y (x + 5)
(b) (x + 5)
(c) 2y
(d) None of these
► (a) 2y (x + 5)

3. Divide as directed: 5 (2x + 1) (3x + 5) ÷ (2x + 1)

(a) 5 (3x + 5)

(b) (3x + 5)

(c) 5

(d) none of these

► (a) 5 (3x + 5)

4. Solve: –20(x)⁴ ÷ 10(x)²

(a) 1/2x

(b) x

(c) 1/2

(d) -2x²

► (d) -2x²

5. Find the common factors of 2y, 22xy.
(a) 2y
(b) 2
(c) 22
(d) y
► (a) 2y

6. Choose the factors of 15x²−26x+8 from the following.

(a) (3x−4),(5x+2)

(b) (3x−4),(5x−2)

(c) (3x+4),(5x−2)

(d) (3x+4),(5x+2)
► (b) (3x−4),(5x−2)

7. Find and correct the errors in the following mathematical statements. x (3x + 2) = 3x² + 2

(a) x (3x + 2) = 3x² + 2x

(b) x (3x + 2) = 3x²

(c) x(3x + 2) = 5x²+ 2x

(d) none of these
► (a) x (3x + 2) = 3x² + 2x

8. Divide as directed: 52pqr (p + q) (q + r) (r + p) ÷104pq (q + r) (r + p)

(a) r(p+q)

(b) 1/2 r(p+q)

(c) 1/2

(d) none of these

► (b) 1/2 r(p+q)

9. Factorise: x²+xy+ 8x+ 8y

(a) (x + 8) (x + y)

(b) (x + y)

(c) (x + 8)

(d) (x + 9) (x – y)
► (a) (x + 8) (x + y)

10. What are the factors of x²+xy−2xz−2yz?

(a) (x−y) and (x+2z)

(b) (x+y) and (x−2z)

(c) (x−y)and (x−2z)

(d) (x+y) and (x+2z)
► (b) (x+y) and (x−2z)

11. Factorize x² + 8x + 12

(a) (x + 2)(x + 6)

(b) (x + 3)(x + 4)

(c) 3x + 12

(d) 3x – 12
► (a) (x + 2)(x + 6)

12. How many factors does (x⁹−x) have?

(a) 5

(b) 4

(c) 2

(d) 9
► (a) 5

13. Which of the following is quotient obtained on dividing –18 xyz² by –3 xz?

(a) 6 yz

(b) –6 yz

(c) 6 xy²

(d) 6 xy
► (a) 6 yz

14. Divide the given polynomial by the given monomial: (5x²− 6x) ÷ 3x

(a) (5x – 6)

(b) 1/3

(c) 1/3(5x – 6)

(d) none of these

► (c) 1/3(5x – 6)

15. Factorise 6xy – 4y + 6 – 9x.

(a) (3x – 2) (2y – 3)

(b) (3x – 2)

(c) (2y – 3)

(d) (2x – 3) (3y – 2)

► (a) (3x – 2) (2y – 3)

16. When we factorise an expression, we write it as a ________ of factors.

(a) product

(b) difference

(c) sum

(d) none of these

► (a) product

17. Factorise: 4y² −12y + 9

(a) (7y− 5)²

(b) (5y− 3)²

(c) (2y− 5)²

(d) (2y− 3)²

► (d) (2y− 3)²

18. Amrit and Pankaj expanded (x−5)². Amrit’s answer is x²−25 and Pankaj’s answer is x²−10x+25. Which of the following statements is correct?
(a) Amrit’s answer is correct.
(b) Pankaj’s answer is wrong.
(c) Both got correct answer.
(d) Pankaj’s answer is correct.
► (d) Pankaj’s answer is correct.

Factorisation Class 8 Extra Questions Very Short Answer Type

Question 1.
Find the common factors of the following terms.
(a) 25x²y, 30xy²
(b) 63m³n, 54mn⁴
Solution:
(a) 25x²y, 30xy²
25x²y = 5 × 5 × x × x × y
30xy² = 2 × 3 × 5 × x × y × y
Common factors are 5× x × y = 5 xy

(b) 63m³n, 54mn⁴
63m³n = 3 × 3 × 7 × m × m × m × n
54mn⁴ = 2 × 3 × 3 × 3 × m × n × n × n × n
Common factors are 3 × 3 × m × n = 9mn

Question 2.
Factorise the following expressions.
(a) 54m³n + 81m⁴n²
(b) 15x²y³z + 25x³y²z + 35x²y²z²
Solution:
(a) 54m³n + 81m⁴n²
= 2 × 3 × 3 × 3 × m × m × m × n + 3 × 3 × 3 × 3 × m × m × m × m × n × n
= 3 × 3 × 3 × m × m × m × n × (2 + 3 mn)
= 27m³n (2 + 3mn)

(b) 15x²y³z + 25 x³y²z + 35x²y²z² = 5x²y²z ( 3y + 5x + 7)

Question 3.
Factorise the following polynomials.
(a) 6p(p – 3) + 1 (p – 3)
(b) 14(3y – 5z)³ + 7(3y – 5z)²
Solution:
(a) 6p(p – 3) + 1 (p – 3) = (p – 3) (6p + 1)
(b) 14(3y – 5z)³ + 7(3y – 5z)²
= 7(3y – 5z)² [2(3y – 5z) +1]
= 7(3y – 5z)² (6y – 10z + 1)

Question 4.
Factorise the following:
(a) p²q – pr² – pq + r²
(b) x² + yz + xy + xz
Solution:
(a) p²q – pr² – pq + r²
= (p²q – pq) + (-pr² + r2)
= pq(p – 1) – r²(p – 1)
= (p – 1) (pq – r²)

(b) x² + yz + xy + xz
= x² + xy +xz + yz
= x(x + y) + z(x + y)
= (x + y) (x + z)

Question 5.
Factorise the following polynomials.
(a) xy(z² + 1) + z(x² + y²)
(b) 2axy² + 10x + 3ay² + 15
Solution:
(a) xy(z² + 1) + z(x² + y²)
= xyz² + xy + 2x² + zy²
= (xyz² + zx²) + (xy + zy²)
= zx(yz + x) + y(x + yz)
= zx(x + yz) + y(x + yz)
= (x + yz) (zx + y)

(b) 2axy² + 10x + 3ay² + 15
= (2axy² + 3ay²) + (10x + 15)
= ay²(2x + 3) +5(2x + 3)
= (2x + 3) (ay² + 5)

Question 6.
Factorise the following expressions.
(а) x² + 4x + 8y + 4xy + 4y²
(b) 4p² + 2q² + p²q² + 8
Solution:
(a) x² + 4x + 8y + 4xy + 4y²
= (x² + 4xy + 4y²) + (4x + 8y)
= (x + 2y)² + 4(x + 2y)
= (x + 2y)(x + 2y + 4)

(b) 4p² + 2q² + p²q² + 8
= (4p² + 8) + (p²q² + 2q²)
= 4(p² + 2) + q²(p² + 2)
= (p² + 2)(4 + q²)

Question 7.
Factorise:
(a) a² + 14a + 48
(b) m² – 10m – 56
Solution:
(a) a² + 14a + 48
= a² + 6a + 8a + 48
[6 + 8 = 14 ; 6 × 8 = 48]
= a(a + 6) + 8(a + 6)
= (a + 6) (a + 8)

(b) m² – 10m – 56
= m² – 14m + 4m – 56
[14 – 4 = 10; 4 × 4 = 56]
= m(m – 14) + 6(m – 14)
= (m – 14) (m + 6)

Question 8.
Factorise:
(a) x⁴ – (x – y)⁴
(b) 4x² + 9 – 12x – a² – b² + 2ab
Solution:
(a) x⁴ – (x – y)⁴
= (x²)² – [(x – y)²]²
= [x² – (x – y)²] [x² + (x – y)²]
= [x + (x – y] [x – (x – y)] [x² + x² – 2xy + y²]
= (x + x – y) (x – x + y)[2x² – 2xy + y²]
= (2x – y) y(2x² – 2xy + y²)
= y(2x – y) (2x² – 2xy + y²)

(b) 4x² + 9 – 12x – a² – b² + 2ab
= (4x² – 12x + 9) – (a² + b² – 2ab)
= (2x – 3)² – (a – b)²
= [(2x – 3) + (a – b)] [(2x – 3) – (a – b)]
= (2x – 3 + a – b)(2x – 3 – a + b)

Factorisation Class 8 Extra Questions Short Answer Type

Question 9.
Factorise the following polynomials.
(a) 16x⁴ – 81
(b) (a – b)² + 4ab
Solution:
(a) 16x⁴ – 81
= (4x²)² – (9)2
= (4x² + 9)(4x² – 9)
= (4x² + 9)[(2x)² – (3)²]
= (4x² + 9)(2x + 3) (2x – 3)

(b) (a – b)² + 4ab
= a² – 2ab + b² + 4ab
= a² + 2ab + b²
= (a + b)²

Question 10.
Factorise:
(а) 14m⁵n⁴p² – 42m⁷n³p⁷ – 70m⁶n⁴p³
(b) 2a²(b² – c²) + b²(2c² – 2a²) + 2c²(a² – b²)
Solution:
(a) 14m⁵n⁴p² – 42m⁷n³p⁷ – 70m⁶n⁴p³
= 14m⁵n³p²(n – 3m²p⁵ – 5mnp)

(b) 2a²(b² – c²) + b²(2c² – 2a²) + 2c²(a² – b²)
= 2a²(b² – c²) + 2b²(c² – a²) + 2c²(a² – b²)
= 2[a²(b² – c²) + b²(c² – a²) + c²(a² – b²)]

= 2 × 0
= 0

Question 11.
Factorise:
(a) (x + y)² – 4xy – 9z²
(b) 25x² – 4y² + 28yz – 49z²
Solution:
(a) (x + y)² – 4xy – 9z²
= x² + 2xy + y² – 4xy – 9z²
= (x² – 2xy + y²) – 9z²
= (x – y)² – (3z)²
= (x – y + 3z) (x – y – 3z)

(b) 25x² – 4y² + 28yz – 49z²
= 25x² – (4y² – 28yz + 49z²)
= (5x)² – (2y – 7)²
= (5x + 2y – 7) [5x – (2y – 7)]
= (5x + 2y – 7) (5x – 2y + 7)

Question 12.
Evaluate the following divisions:
(a) (3b – 6a) ÷ (30a – 15b)
(b) (4x² – 100) ÷ 6(x + 5)
Solution:

Question 13.
Simplify the following expressions:

Solution:

Question 14.
Factorise the given expressions and divide that as indicated.
(a) 39n³(50n² – 98 ) ÷ 26n²(5n – 7)
(b) 44(p⁴ – 5p³ – 24p²) ÷ 11p(p – 8)
Solution:

Question 15.
If one of the factors of (5x² + 70x – 160) is (x – 2). Find the other factor.
Solution:
Let the other factor be m.
(x – 2) × m = 5x² + 70x – 160

MCQ Questions for Class 8 Maths: Ch 13 Direct and Inverse Proportions

1. A garrison of 500 persons had provisions for 27 days. After 3 days a reinforcement of 300 persons arrived. For how many more days will the remaining food last now?

(a) 12 days

(b) 14 days

(c) 16 days

(d) 15 days

► (d) 15 days

2. When one quantity is increased, the other quantity is also increased. This proportion is called _______

(a) Kally proportion

(b) Direct proportion

(c) Inverse proportion

(d) None of these

► (b) Direct proportion

3. 72 books are packed in 4 cartons of the same size. How many cartons are required for 360 books?

(a) 22

(b) 18

(c) 20

(d) None of these

► (c) 20

4. 8 g of sandal wood cost Rs 40. What will 10 g cost ?

(a) Rs 30

(b) Rs 36

(c) Rs 48

(d) Rs 50

► (d) Rs 50

5. The price of 357 mangoes is Rs.1517.25. What will be the approximate price of 49 dozens of such mangoes?

(a) Rs.3000

(b) Rs.3500

(c) Rs.4000

(d) Rs.2500

► (a) Rs.3000

6. 6 pipes are required to fill a tank in 1 hour 20 minutes. How long will it take if only 5 pipes of the same type are used?

(a) 56 minutes

(b) 72 minutes

(c) 96 minutes

(d) 80 minutes

► (c) 96 minutes

7. A van covers 432 km with 36 litres of diesel. How much distance would it cover with 25 litres of diesel?

(a) 200 km

(b) 300 km

(c) 100 km

(d) 350 km

► (b) 300 km

8. 120 copies of a book cost Rs 600. What will 400 copies cost ?

(a) Rs 1000

(b) Rs 2000

(c) Rs 3000

(d) Rs 2400

► (b) Rs 2000

9. A boy runs 1 km in 10 minutes. How long will he take to ran 600 m ?

(a) 2 minutes

(b) 3 minutes

(c) 4 minutes

(d) 6 minutes

► (d) 6 minutes

10. The cost of 5 metres of a particular quality of cloth is Rs 210. Find the cost of 2 metres of cloth of the same type.

(a) Rs 100

(b) Rs 84

(c) Rs 90

(d) Rs 60

► (b) Rs 84

11. An electric pole, 14 metres high, casts a shadow of 10 metres. Find the height of a tree that casts a shadow of 15 metres under similar conditions.

(a) 21 metres

(b) 30 metres

(c) 25 metres

(d) None of these

► (a) 21 metres

12. A can do a certain work in the same time in which B and C together can do it. If A and B together could do it in 10 days and C alone in 50 days, then B alone could do it in:

(a) 15 days

(b) 20 days

(c) 25 days

(d) 30 days

► (c) 25 days

13. The scale of a map is 1:3×10⁷ Two cities are 5 cm apart on the map. Find the actual distance between them in kilometres.

(a) 1500 km

(b) 1000 km

(c) 1100 km

(d) 2000 km
► (a) 1500 km

14. A journey by bus takes 45 minutes at 40 km/hour. How fast must a car go to undertake the same journey in 25 minutes?

(a) 36 km/h

(b) 48 km/h

(c) 72 km/h

(d) None of these

► (c) 72 km/h

15. Raju earns Rs 1440, if he works for 12 days. If he works for 30 days, he will earn

(a) Rs 2400

(b) Rs 3600

(c) Rs 4800

(d) None of these

► (b) Rs 3600

16. x varies inversely as square of y. Given that y = 3 for x = 1.find the value of x for y = 4.

(a) 3

(b) 9

(c) 1/3

(d) 9/16

► (d) 9/16

17. If the cost of 27 bags of paddy is Rs.9450, what is the cost of 36 bags of paddy?

(a) Rs.12000

(b) Rs.12600

(c) Rs.16200

(d) Rs.10620

► (b) Rs.12600

18. 36 men can complete a piece of work in 18 days. In how many days will 27 men complete the same work ?

(a) 24 days

(b) 28 days

(c) 34 days

(d) 35 days

► (a) 24 days

19. If 3 men or 6 women can do a piece of work in 16 days, in how many days can 12 men and 8 women do the same piece of work?

(a) 4 days

(b) 5 days

(c) 3 days

(d) 2 days

► (c) 3 days

20. There is enough food to last for 40 people for 10 days. If 10 more people join them, the food will last for

(a) 10 days

(b) 12 days

(c) 8 days

(d) None of these

► (c) 8 days

21. A mixture of paint is prepared by mixing 1 part of red pigments with 8 parts of base. How many parts of base will be used in mixture by mixing 7 part of red pigment?

(a) 70

(b) 56

(c) 63

(d) 49

► (b) 56

22. Two quantities x and y are said to be in ___________ if they increase (decrease) together in such a manner that the ratio of their corresponding values remains constant.

(a) inverse proportion

(b) mix proportion

(c) direct proportion

(d) None of these

► (c) direct proportion

important questions

Question 1:

Observe the tables given below and in each one find whether x and y are proportional:
(i)

x	3	5	8	11	26
y	9	15	24	33	78

(ii)

x	2.5	4	7.5	10	14
y	10	16	30	40	42

(iii)

x	5	7	9	15	18	25
y	15	21	27	60	72	75

ANSWER:

(i)
Clearly, xy=39=515=824=1133=2678=13(constant)Therefore, x and y are proportional.Clearly, xy=39=515=824=1133=2678=13(constant)Therefore, x and y are proportional.

(ii)
 Clearly, xy=2.510=416=7.530=1040=14, while 1442=13i.e., 2.510=416=7.530=1040is not equal to 1442.Therefore, x and y are not proportional.Clearly, xy=2.510=416=7.530=1040=14, while 1442=13i.e., 2.510=416=7.530=1040is not equal to 1442.Therefore, x and y are not proportional.

(iii)
 Clearly, xy=515=721=927=2575=13, while 1560=1872=14i.e., 515=721=927=2575is not equal to 1560 and1872.Therefore, x and y are not proportional.Clearly, xy=515=721=927=2575=13, while 1560=1872=14i.e., 515=721=927=2575is not equal to 1560 and1872.Therefore, x and y are not proportional.

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Question 2:

If x and y are directly proportional, find the values of x₁ , x₂ and y₁ in the table given below:

x	3	x1	x2	10
y	72	120	192	y1

ANSWER:

Since x and y are directly propotional, we have: 372=x1120=x2192=10y1Now, 372=x1120⇒x1=120×372 = 5Since x and y are directly propotional, we have: 372=x1120=x2192=10y1Now, 372=x1120⇒x1=120×372 = 5

And, 372 = x2192   ⇒ x2 = 3 × 19272 = 8And, 372 = x2192   ⇒ x2 = 3 × 19272 = 8
And, 372=10y1⇒y1=72×103=240And, 372=10y1⇒y1=72×103=240
Therefore, x1 = 5, x2 = 8 and y1 = 240Therefore, x1 = 5, x2 = 8 and y1 = 240

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Question 3:

A truck covers a distance of 510 km in 34 litres of diesel. How much distance would it cover in 20 litres of diesel?

ANSWER:

Let the required distance be x km. Then, we have:

Quantity of diesel (in litres)	34	20
Distance (in km)	510	x

Clearly, the less the quantity of diesel consumed, the less is the distance covered.
So, this is a case of direct proportion.
Now, 34510=20x⇒115=20x⇒x×1=20×15=300Now, 34510=20x⇒115=20x⇒x×1=20×15=300

Therefore, the required distance is 300 km.

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Question 4:

A taxi charges a fare of Rs 2550 for a journey of 150 km. How much would it charge for a journey of 124 km?

ANSWER:

Let the charge for a journey of 124 km be ₹x.

Price(in ₹)	2550	x
Distance(in km)	150	124

More is the distance travelled, more will be the price.
So, it is a case of direct proportion.
∴2550150=x124⇒x=2550×124150=2108∴2550150=x124⇒x=2550×124150=2108
Thus, the taxi charges ₹2,108 for the distance of 124 km.

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Question 5:

A loaded truck covers 16 km in 25 minutes. At the same speed, how far can it travel in 5 hours?

ANSWER:

Let the required distance be x km. Then, we have:
1 h=60 mini.e., 5 h=5×60=300 min1 h=60 mini.e., 5 h=5×60=300 min.

Distance (in km)	16	x
Time (in min)	25	300

Clearly, the more the time taken, the more will be the distance covered.

So, this is a case of direct proportion.
Now, 1625=x300⇒x=(16×30025)⇒x = 192Now, 1625=x300⇒x=16×30025⇒x = 192
Therefore, the required distance is 192 km.

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Question 6:

If 18 dolls cost Rs 630, how many dolls can be bought for Rs 455?

ANSWER:

Let the required number of dolls be x. Then, we have:
 

No of dolls	18	x
Cost of dolls (in rupees)	630	455

Clearly, the less the amount of money, the less will be the number of dolls bought.
So, this is a case of direct proportion.
Now, 18630=x455⇒135=x455⇒x=45535⇒x=13Now, 18630=x455⇒135=x455⇒x=45535⇒x=13

Therefore, 13 dolls can be bought for Rs 455.

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Question 7:

If 9 kg of sugar costs ₹ 238.50, how much sugar can be bought for ₹ 371?

ANSWER:

Let the quantity of sugar bought for ₹371 be x kg.

Quantity(in kg)	9	x
Price(in ₹)	238.50	371

The price increases as the quantity increases. Thus, this is a case of direct proportion.
∴9238.50=x371⇒x=9×371238.50=14∴9238.50=x371⇒x=9×371238.50=14
Thus, the quantity of sugar bought for ₹371 is 14 kg.

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Question 8:

The cost of 15 metres of a cloth is Rs 981. What length of this cloth can be purchased for Rs 1308?

ANSWER:

Let the length of cloth be x m. Then, we have:
​

Length of cloth (in metres)	15	x
Cost of cloth (in rupees)	981	1308

Clearly, more length of cloth can be bought by more amount of money.
So, this is a case of direct proportion.
Now, 15981=x1308⇒x=15×1308981⇒x=20Now, 15981=x1308⇒x=15×1308981⇒x=20

Therefore, 20 m of cloth can be bought for Rs 1,308.

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Question 9:

In a model of a ship, the mast is 9 cm high, while the mast of the actual ship is 15m high. If the length of the ship is 35 metres, how long is the model ship?

ANSWER:

Let x m be the length of the model of the ship. Then, we have:
1 m = 100 cmTherefore, 15 m= 1500 cm35 m= 3500 cm1 m = 100 cmTherefore, 15 m= 1500 cm35 m= 3500 cm
 

	Length of the mast (in cm)	Length of the  ship (in cm)
Actual ship	1500	3500
Model of the ship	9	x

Clearly, if the length of the actual ship is more, then the length of the model ship will also be more.
So, this is a case of direct proportion.
Now, 15009=3500x⇒x=3500×91500⇒x=21 cmNow, 15009=3500x⇒x=3500×91500⇒x=21 cm
Therefore, the length of the model of the ship is 21 cm.

Page No 163:

Question 10:

In 8 days, the earth picks up (6.4 × 10⁷) kg of dust from the atmosphere. How much dust will it pick up in 15 days?

ANSWER:

Let x kg be the required amount of dust. Then, we have:
 

No. of days	8	15
Dust (in kg)	6.4×1076.4×107	x

Clearly, more amount of dust will be collected in more number of days.
So, this is a case of direct proportion.
Now, 86.4×107=15x⇒x=15×6.4×1078⇒x=12×107Now, 86.4×107=15x⇒x=15×6.4×1078⇒x=12×107

Therefore, 12,00,00,000 kg of dust will be picked up in 15 days.

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Question 11:

A car is travelling at the average speed of 50 km/hr. How much distance would it travel in 1 hour 12 minutes?

ANSWER:

Let x km be the required distance. Then, we have:

1 h=60 mini.e., 1h 12 min=(60+12) min=72 min1 h=60 mini.e., 1h 12 min=(60+12) min=72 min
 

Distance covered (in km)	50	x
Time (in min)	60	72

Clearly, more distance will be covered in more time.
So, this is a case of direct proportion.
Now, 5060=x72⇒x=50×7260⇒x=60Now, 5060=x72⇒x=50×7260⇒x=60
Therefore, the distance travelled by the car in 1 h 12 min is 60 km.

Page No 163:

Question 12:

Ravi walks at the uniform rate of 5 km/hr. What distance would he cover in 2 hours 24 minutes?

ANSWER:

Let x km be the required distance covered by Ravi in 2 h 24 min.
Then, we have:
1 h=60mini.e., 2 h 24 min=(120+24) min=144 min1 h=60mini.e., 2 h 24 min=(120+24) min=144 min
 

Distance covered (in km)	5	x
Time (in min)	60	144

Clearly, more distance will be covered in more time.
So, this is a case of direct proportion.
Now,560=x144⇒x=5×14460⇒x=12Now,560=x144⇒x=5×14460⇒x=12

Therefore, the distance covered by Ravi in 2 h 24 min is 12 km.

Page No 163:

Question 13:

If the thickness of a pile of 12 cardboards is 65 mm, find the thickness of a pile of 312 such cardboards.

ANSWER:

Let x mm be the required thickness. Then, we have:
 

Thickness of cardboard (in mm)	65	x
No. of cardboards	12	312

Clearly, when the number of cardboard is more, the thickness will also be more.
So, it is a case of direct proportion.
Now, 6512=x312⇒x=65×31212⇒x=1690Now, 6512=x312⇒x=65×31212⇒x=1690

Therefore, the thickness of the pile of 312 cardboards is 1690 mm.

Page No 163:

Question 14:

11 men can dig 634634-metre-long trench in one day. How many men should be employed for digging 27-metre-long trench of the same type in one day?

ANSWER:

Let x be the required number of men.

Now, 634 m=274 mNow, 634 m=274 m

Then, we have:

Number of men	11	x
Length of trench (in metres)	274274	27

Clearly, the longer the trench, the greater will be the number of men required.
So, it is a case of direct proportion.
Now, 11274=x27⇒11×427=x27⇒x=44Now, 11274=x27⇒11×427=x27⇒x=44

Therefore, 44 men should be employed to dig a trench of length 27 m.

Page No 163:

Question 15:

Reenu types 540 words during half an hour. How many words would she type in 8 minutes?

ANSWER:

Let Reenu type x words in 8 minutes.
 

No. of words	540	x
Time taken (in min)	30	8

Clearly, less number of words will be typed in less time. 
So, it is a case of direct proportion.
Now,54030=x8⇒x=540×830⇒x=144Now,54030=x8⇒x=540×830⇒x=144

Therefore, Reenu will type 144 words in 8 minutes.

Page No 165:

Question 1:

Observe the tables given below and in each case find whether x and y are inversely proportional:
(i)

x	6	10	14	16
y	9	15	21	24

(ii)

x	5	9	15	3	45
y	18	10	6	30	2

(iii)

x	9	3	6	36
y	4	12	9	1

ANSWER:

(i)
Clearly, 6×9≠ 10×15 ≠ 14×21≠ 16×24Therefore, x and y are not inversely proportional.Clearly, 6×9≠ 10×15 ≠ 14×21≠ 16×24Therefore, x and y are not inversely proportional.

(ii)
Clearly, 5×18= 9×10=15×6=3×30=45×2=90=(consant)Therefore, x and y are inversely proportional.Clearly, 5×18= 9×10=15×6=3×30=45×2=90=(consant)Therefore, x and y are inversely proportional.

(iii)
Clearly, 9×4=3×12=36×1=36, while 6×9=54i.e., 9×4=3×12=36×1≠6×9Therefore, x and y are not inversely proportional.Clearly, 9×4=3×12=36×1=36, while 6×9=54i.e., 9×4=3×12=36×1≠6×9Therefore, x and y are not inversely proportional.

Page No 165:

Question 2:

If x and y are inversely proportional, find the values of x₁, x₂, y₁ and y₂ in the table given below:

x	8	x1	16	x2	80
y	y1	4	5	2	y2

ANSWER:

 Since x and y are inversely proportional, xy must be a constant.Since x and y are inversely proportional, xy must be a constant.
Therefore, 8×y1=x1×4=16×5=x2×2=80×y2Now, 16×5=8×y1⇒808=y1∴ y1=1016×5=x1×4⇒804=x1∴ x1=2016×5=x2×2⇒802=x2∴ x2=4016×5=80×y2⇒8080=y2∴ y2=1Hence, y1=10, x1=20, x2=40 and y2=1Therefore, 8×y1=x1×4=16×5=x2×2=80×y2Now, 16×5=8×y1⇒808=y1∴ y1=1016×5=x1×4⇒804=x1∴ x1=2016×5=x2×2⇒802=x2∴ x2=4016×5=80×y2⇒8080=y2∴ y2=1Hence, y1=10, x1=20, x2=40 and y2=1

Page No 165:

Question 3:

If 35 men can reap a field in 8 days, in how many days can 20 men reap the same field?

ANSWER:

Let x be the required number of days. Then, we have:
 

No. of days	8	x
No. of men	35	20

Clearly, less men will take more days to reap the field.
So, it is a case of inverse proportion.

Now, 8 × 35=x × 20⇒8 × 3520=x⇒14=xNow, 8 × 35=x × 20⇒8 × 3520=x⇒14=x

Therefore, 20 men can reap the same field in 14 days.

Page No 165:

Question 4:

12 men can dig a pond in 8 days. How many men can dig it in 6 days?

ANSWER:

Let x be the required number of men. Then, we have:
 

No. of days	8	6
No. of men	12	x

Clearly, more men will require less number of days to dig the pond.
So, it is a case of inverse proportion.
Now, 8 × 12 = 6 × x⇒x=8 × 126 ⇒x=16Now, 8 × 12 = 6 × x⇒x=8 × 126 ⇒x=16

Therefore, 16 men can dig the pond in 6 days.

Page No 166:

Question 5:

6 cows can graze a field in 28 days. How long would 14 cows take to graze the same field?

ANSWER:

Let x be the number of days. Then, we have:
 

No. of days	28	x
No. of cows	6	14

Clearly, more number of cows will take less number of days to graze the field.
So, it is a case of inverse proportion.
Now, 28 × 6 = x × 14⇒x=28 × 614 ⇒x=12Now, 28 × 6 = x × 14⇒x=28 × 614 ⇒x=12

Therefore, 14 cows will take 12 days to graze the field.

Page No 166:

Question 6:

A car takes 5 hours to reach a destination by travelling at the speed of 60 km/hr. How long will it take when the car travels at the speed of 75 km/hr?

ANSWER:

Let x h be the required time taken. Then, we have:
 

Speed (in km/h)	60	75
Time (in h)	5	x

Clearly, the higher the speed, the lesser will be the the time taken.
So, it is a case of inverse proportion.
Now, 60×5=75×x⇒x=60×575⇒x=4Now, 60×5=75×x⇒x=60×575⇒x=4

Therefore, the car will reach its destination in 4 h if it travels at a speed of 75 km/h.

Page No 166:

Question 7:

A factory requires 42 machines to produce a given number of articles in 56 days. How many machines would be required to produce the same number of articles in 48 days?

ANSWER:

Let x be the number of machines required to produce same number of articles in 48.
Then, we have:
 

No. of machines	42	x
No. of days	56	48

Clearly, less number of days will require more number of machines.
So, it is a case of inverse proportion.
Now, 42×56=x×48⇒x=42×5648⇒x=49Now, 42×56=x×48⇒x=42×5648⇒x=49

Therefore, 49 machines would be required to produce the same number of articles in 48 days.

Page No 166:

Question 8:

7 teps of the same size fill a tank in 1 hour 36 minutes. How long will 8 taps of the same size take to fill the tank?

ANSWER:

Let x be the required number of taps. Then, we have:
1 h = 60 min
i.e., 1 h 36 min = (60+36) min = 96 min
 

No. of taps	7	8
Time (in min)	96	x

Clearly, more number of taps will require less time to fill the tank.
So, it is a case of inverse proportion.
Now, 7×96=8×x⇒x=7×968⇒x=84Now, 7×96=8×x⇒x=7×968⇒x=84

Therefore, 8 taps of the same size will take 84 min or 1 h 24 min to fill the tank.

Page No 166:

Question 9:

8 taps of the same size fill a tank in 27 minutes. If two taps go out of order, how long would the remaining taps take to fill the tank?

ANSWER:

Let x min be the required number of time. Then, we have:

No. of taps	8	6
Time (in min)	27	xx

Clearly, less number of taps will take more time to fill the tank .
So, it is a case of inverse proportion.

Now, 8×27=6×x⇒x=8×276⇒x=36Now, 8×27=6×x⇒x=8×276⇒x=36

Therefore, it will take 36 min to fill the tank.

Page No 166:

Question 10:

A farmer has enough food to feed 28 animals in his cattle for 9 days. How long would the food last, if there were 8 more animals in his cattle?

ANSWER:

Let x be the required number of days. Then, we have:

No. of days	9	x
No. of animals	28	36

Clearly, more number of animals will take less number of days to finish the food.
So, it is a case of inverse proportion.
Now, 9×28=x×36⇒x=9×2836⇒x=7Now, 9×28=x×36⇒x=9×2836⇒x=7

Therefore, the food will last for 7 days.

Page No 166:

Question 11:

A garrison of 900 men had provisions for 42 days. However, a reinforcement of 500 men arrived. For how many days will the food last now?

ANSWER:

Let x be the required number of days. Then, we have:
 

No. of men	900	1400
No. of days	42	x

Clearly, more men will take less number of days to finish the food.
So, it is a case of inverse proportion.

Now, 900×42=1400×x⇒x=900×421400⇒x=27Now, 900×42=1400×x⇒x=900×421400⇒x=27

Therefore, the food will now last for 27 days.

Page No 166:

Question 12:

In a hostel, 75 students had food provision for 24 days. If 15 students leave the hostel, for how many days would the food provision last?

ANSWER:

Let x be the required number of days. Then, we have:
 

No. of students	75	60
No. of days	24	x

Clearly, less number of students will take more days to finish the food.
So, it is a case of inverse proportion.
Now, 75×24=60×x⇒x=75×2460⇒x=30Now, 75×24=60×x⇒x=75×2460⇒x=30

Therefore, the food will now last for 30 days.

Page No 166:

Question 13:

A school has 9 periods a day each of 40 minutes duration. How long would each period be, if the school has 8 periods a day, assuming the number of school hours to be the same?

ANSWER:

Let x min be the duration of each period when the school has 8 periods a day.

No. of periods	9	8
Time (in min)	40	x

Clearly, if the number of periods reduces, the duration of each period will increase.
So, it is a case of inverse proportion.
Now, 9×40=8×x⇒x=9×408⇒x=45Now, 9×40=8×x⇒x=9×408⇒x=45

Therefore, the duration of each period will be 45 min if there were eight periods a day.

Page No 166:

Question 14:

If x and y vary inversely and x = 15 when y = 6, find y when x = 9.

ANSWER:

xx	15	9
yy	6	y1y1

x and y vary inversely.i.e. xy = constantNow, 15×6=9×y1⇒y1=15×69⇒y1=10x and y vary inversely.i.e. xy = constantNow, 15×6=9×y1⇒y1=15×69⇒y1=10

∴ Value of y=10y=10, when x =9

Page No 166:

Question 15:

If x and y vary inversely and x = 18 when y = 8, find x when y = 16.

ANSWER:

xx	18	x1x1
yy	8	16

x and y vary inversely.i.e. xy = constantNow, 18×8=x1×16⇒18×816=x1⇒9=x1x and y vary inversely.i.e. xy = constantNow, 18×8=x1×16⇒18×816=x1⇒9=x1

∴ Value of x=9x=9

Page No 166:

Question 1:

If 14 kg of pulses cost ₹ 882, what is the cost of 22 kg of pulses?
(a) ₹ 1254
(b) ₹ 1298 
(c) ₹ 1342
(d) ₹ 1386

ANSWER:

Let 22 kg of pulses cost ₹x.

Quantity(in kg)	14	22
Price(in ₹)	882	x

As the quantity increases, the price also increases. So, it is a case of direct proportion.
∴14882=22x⇒x=22×88214=1386∴14882=22x⇒x=22×88214=1386
Thus, the cost of 22 kg of pulses is ₹1,386.

Hence, the correct answer is option (d).

Page No 166:

Question 2:

If 8 oranges cost ₹ 52, how many oranges can be bought for ₹ 169?
(a) 13
(b) 18
(c) 26
(d) 24

ANSWER:

Let the number of oranges that can be bought for ₹169 be x.

Quantity	8	x
Price(in ₹)	52	169

As the quantity increases the price also increases. So, this is a case of direct proportion.
∴852=x169⇒x=8×16952=26∴852=x169⇒x=8×16952=26
Thus, 26 oranges can be bought for ₹169.

Hence, the correct answer is option (c).

Page No 166:

Question 3:

Tick (✓) the correct answer:
A machine fills 420 bottles in 3 hours. How many bottles will it fill in 5 hours?
(a) 252
(b) 700
(c) 504
(d) 300

ANSWER:

(b) 700

Let x be the number of bottles filled in 5 hours.
 

No. of bottles	420	xx
Time (h)	3	5

More number of bottles will be filled in more time.

Now, 4203=x5⇒x=420×53⇒x=700Now, 4203=x5⇒x=420×53⇒x=700

Therefore, 700 bottles would be filled in 5 h.

Page No 166:

Question 4:

Tick (✓) the correct answer:
A car is travelling at a uniform speed of 75 km/hr. How much distance will it cover in 20 minutes?
(a) 25 km
(b) 15 km
(c) 30 km
(d) 20 km

ANSWER:

(a) 25 km

Let x km be the required distance.
Now, 1 h = 60 min
 

Distance (in km)	75	xx
Time (in min)	60	20

Less distance will be covered in less time.
Now, 7560=x20⇒x=75×2060⇒x=25 kmNow, 7560=x20⇒x=75×2060⇒x=25 km

Page No 166:

Question 5:

Tick (✓) the correct answer:
The weight of 12 sheets of a thick paper is 40 grams. How many sheets would weight 1 kg?
(a) 480
(b) 360
(c) 300
(d) none of these

ANSWER:

(c) 300
Let x sheets weigh 1 kg.
Now, 1 kg = 1000 g

No. of sheets	12	xx
Weight (in  g)	40	1000

Now, 1240=x1000⇒x=12×100040⇒x=300Now, 1240=x1000⇒x=12×100040⇒x=300

Page No 166:

Question 6:

Tick (✓) the correct answer:
A pole 14 m high casts a shadow of 10 m. At the same time, what will be the height of a tree, the length of whose shadow is 7 metres?
(a) 20 m
(b) 9.8 m
(c) 5 m
(d) none of these

ANSWER:

(b) 9.8 m
Let x m be the height of the tree.

Height of object	14	xx
Length of shadow	10	7

The more the length of the shadow, the more will be the height of the tree.
Now, 1410=x7⇒x=14×710⇒x=9.8Now, 1410=x7⇒x=14×710⇒x=9.8

Therefore, a 9.8 m tall tree will cast a shadow of length 7 m.

Page No 167:

Question 7:

Tick (✓) the correct answer:
A photograph of a bacteria enlarged 50000 times attains a length of 5 cm. The actual length of bacteria is
(a) 1000 cm
(b) 10⁻³ cm
(c) 10⁻⁴ cm
(d) 10⁻² cm

ANSWER:

(c) 10−4 cm10-4 cm
Let x cm be the actual length of the bacteria.
The larger the object, the larger its image will be.
Now, x1=550000=10−4 cmNow, x1=550000=10-4 cm

Hence, the actual length of the bacteria is ​10−4 cm10-4 cm.

Page No 167:

Question 8:

Tick (✓) the correct answer:
6 pipes fill a tank in 120 minutes, then 5 pipes will fill it in
(a) 100 min
(b) 144 min
(c) 140 min
(d) 108 min

ANSWER:

(b) 144 min
Let x min be the time taken by 5 pipes to fill the tank.

No. of pipes	6	5
Time (in min)	120	xx

Now, 6×120=5×x⇒x=144 Now, 6×120=5×x⇒x=144 

Therefore, 5 pipes will take 144 min to fill the tank.

Page No 167:

Question 9:

Tick (✓) the correct answer:
3 persons can build a wall in 4 days, then 4 persons can build it in
(a) 513513 days
(b) 3 days
(c) 413413 days
(d) none of these

ANSWER:

(b) 3 days
Let x be number of days taken by 4 persons to build the wall.

No. of persons	3	4
No. of days	4	xx

More number of persons will take less time to build the wall.
So, it is a case of inverse proportion.

Now, 3×4=4×x⇒x=3  Now, 3×4=4×x⇒x=3  

Therefore, 4 persons can build the wall in 3 days.

Page No 167:

Question 10:

Tick (✓) the correct answer:
A car takes 2 hours to reach a destination by travelling at 60 km/hr. How long will it take while travelling at 80 km/hr?
(a) 1 hr 30 min
(b) 1 hr 40 min
(c) 2 hrs 40 min
(d) none of these

ANSWER:

(a) 1 h 30 min
Let x h be the time taken by the car travelling at 80 km/hr.
 

Speed (km/h)	60	80
Time (in h)	2	xx

The greater the speed, the lesser will be the time taken.So, it is a case of inverse proportion.Now, 60×2= 80×x⇒x= 12080⇒x= 1.5Therefore, the car will take 1 h 30 min to reach its destination if it travels at a speed of 80 km/h.The greater the speed, the lesser will be the time taken.So, it is a case of inverse proportion.Now, 60×2= 80×x⇒x= 12080⇒x= 1.5Therefore, the car will take 1 h 30 min to reach its destination if it travels at a speed of 80 km/h.

Page No 168:

Question 1:

350 boxes can be placed in 25 cartons. How many boxes can be placed in 16 cartons?

ANSWER:

Let x be the required number of boxes.

No. of boxes	350	xx
No. of cartons	25	16

Less number of boxes will require less number of cartons. 
So, it is a case of direct proportion.
Now, 35025=x16⇒x=350×1625⇒x=224Now, 35025=x16⇒x=350×1625⇒x=224

∴ 224 boxes can be placed in 16 cartoons.

Page No 168:

Question 2:

The cost of 140 tennis balls is Rs 4900. Find the cost of 2 dozen such balls.

ANSWER:

Let Rs x be the cost of 24 tennis balls.

No. of balls	140	24
Cost of balls	4900	xx

More tennis balls will cost more.
Now, 1404900=24x⇒x=24×4900140⇒x=840Now, 1404900=24x⇒x=24×4900140⇒x=840

∴ The cost of 2 dozen tennis balls is Rs 840.

Page No 168:

Question 3:

The railway fare for 61 km is Rs 183. Find the fare for 53 km.

ANSWER:

Let Rs x be the railway fare for a journey of distance 53 km.

Distance (in km)	61	53
Railway fare (in rupees)	183	xx

The lesser the distance, the lesser will be the fare.
So, it is a case of direct proportion .
Now, 61183=53x⇒x=53×18361⇒x=159Now, 61183=53x⇒x=53×18361⇒x=159

The railway fare for a journey of distance 53 km is Rs 159.