Question.1 What the minimum conditions of a democratic election?
Answer:
The minimum conditions of a democratic elections are:

• Everyone should be able to choose. This means that everyone should have one vote and every vote should have equal value.
• There should be something to choose from. Parties and candidates should be free to contest elections and should offer some real choice to the voters.
• The choice should be offered at regular intervals. Elections must be held regularly after every few years.
• The candidate preferred by the people should get elected.
• Elections should be conducted in a free and fair manner where people can choose them at their will. (Any three)

Question 2
“Election campaigns are needed to regulate”. Why?
Answer:
It is sometimes necessary to regulate campaigns to ensure that every political party and candidate gets a fair and equal chance to compete.
According to our election law, no party or candidate can:

• Bribe or threaten voters.
• Appeal to them in the name of caste or religion.
• Use government resources for election campaign.
• Spend more than? 25 lakh in a constituency for a Lok Sabha election or? 10 lakh in a constituency in an assembly election.

Question 3
What is the ‘Model code of Conduct’ for election campaign?
Answer:
According to the medal code of conduct, no party or candidate can:

• Use any place of worship for election propaganda. ‘
• Use government vehicles, aircrafts and officials for election.
• Once elections are announced, the Ministers shall not lay foundation stones of any projects, take any big policy decisions or make any promises of providing public facilities.

Question 4
Why should elections be held regularly?
Answer:
Elections should be held regularly because:

• Elections should be held regularly because it provides incentives to the political parties and leaders.
• They know that if they raise-issues that people want to raised, it would make them popular and increase their chances of victory in the next elections.
• But, if they fail to satisfy the voters with their work, they will not be able to win again.

Question 5 What are the challenges to free and fair elections in India?
Answer:
The elections in India are basically free and fair. But, a few candidates may win purely based on money power and unfair means. These challenges exist not just in India but also in many established democracies. These deeper issues are a matter of concern for those who believe in democracy. The challenges to free and fair elections in India are as follows.

• Candidates and parties with a lot of money may not be sure of their victory but they do enjoy a big and unfair advantage over smaller parties and independents.
• In some parts of the country, candidates with criminal connection have been able to push others out of the electoral race and to secure a ‘ticket’ from major parties.
• Some families tend to dominate political parties; tickets are distributed to relatives from these families.
• Very often elections offer little choice to ordinary citizens, for both the major parties are quite similar to each other both in policies and practice.
• Smaller parties and independent candidates suffer a huge disadvantage compared to bigger parties.

Question 6
How can you say that the outcome of elections is a final test of free and fair elections? Explain
Answer:
One final test of the free and fair of election has in the outcome itself. If elections are not free or fair, the outcome always favours the powerful. In such a situation, the ruling parties do not lose elections. Usually, the losing party does not accept the outcome of a rigged election.
The outcome of India’s elections speaks for itself:

• The ruling parties routinely lose elections in India both at the national and state level. In fact, in every two out of the three elections held in the last fifteen years, the ruling party lost.
• In the US, an incumbent or ‘sitting’ elected representative rarely loses an election. In India, about half of the sitting MPs or MLAs lose elections.
• Candidates who are known to have spent a lot of money on ‘buying votes’ and
  those with known criminal connections often lose elections.
• Barring very few disputed elections, the electoral outcomes are usually accepted as ‘people’s verdict’ by the defeated party.

Question 7
What do you mean by Voter’s List? What is its significance?
Answer:
(i) In a democratic election, the list of those who are eligible to vote is prepared much before the election and given to everyone. This list is officially called the Electoral Roll and is commonly known as the Voters’ List.
(ii) The significance of Voter’s List is as follows:

• This is an important step for it is linked to the first condition of a democratic election. Everyone should get an equal opportunity to choose representatives.
• In our country, all the citizens aged 18 years and above can vote in an election. Every citizen has the right to vote, regardless of his or her caste, religion or gender.
• It is the responsibility of the government to get the names of all the eligible voters put on the Voter’s List. As new persons attain voting age, names are added to the voters’ list. Names of those who move out of a place or those who are dead are deleted.
• A complete revision of the list takes place every five years. This is done to ensure that it remains up to date. In the last few years a new system of Election Photo Identity Card (EPIC) has been introduced. The government has tried to give this card to every person on the voters’ list. But the card is not yet compulsory for voting. For voting, the voters can show many other proofs of identity like the ration card or the driving licence.

Question 8
Explain the role of the Election Commission in conducting the free and fair elections.
Answer:
The role of the Election Commission in conducting the free and fair elections is as follows.

• Election Commission takes decisions on every aspect of conduct and control of elections from the announcement of elections to the declaration of results.
• It implements the Code of Conduct and punishes any candidate or party that violates it.
• It allots election symbols to parties and independent candidates.
• During the election period, the Election Commission can order the government to follow some guidelines, to prevent use and misuse of governmental power to enhance its chances to win elections, or to transfer some government officials.
• When on election duty, government officers work under the control of the Election Commission and not the government.

Question 9
What are the changing trends of people’s participation in elections in India?
Answer:
The changing trends of people’s participation in elections in India are as follows:

• People’s participation in election is usually measured by voter turnout figures. Turnout indicates the per cent of eligible voters who cast their vote. In India, the turnout figures over last few decades have either remained stable or gone up.
• In India, the poor, illiterate and underprivileged people vote in larger proportion as compared to the rich and privileged sections. This is in contrast to western democracies.
• Common people in India attach a lot of importance to elections. They feel that through elections, they can bring pressure on political parties to adopt policies and programmes favourable to them.
• The interest of voters in election-related activities has been increasing over the years. During the 2004 elections, more than one-third voters took part in a campaign-related activity.
• More than half of the people identified themselves as being close to one or the other political party. One out of every seven voters is a member of a political party.

Question 10.
What are the minimum conditions needed for a democratic election?
Solution:
There are five minimum conditions needed for a democratic election. They are :

• Everyone should have the right to vote and every vote should have equal value.
• Parties and candidates should be free to contest elections and they should offer some real choice to the voters.
• Elections must be held regularly .
• Candidates preferred by the people should be elected.
• Elections should be conducted in a free and fair manner.

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QUESTION .1 Enumerate the advantages of mixed farming.
Answer:
Following are the main advantages of mixed farming:

• Farmyard manure is made available from livestock which is used again in agricultural farms.
• Organic waste materials like straw, husks and chaffs of grains, household kitchen waste, etc., are converted into human food through the agency of cattle, sheep, poultry, pigs, etc., as per the choice of farmer.
• It provides work to all the members of a family throughout the year, thus providing subsidiary occupation without the need of employing special labour.
• Adopting exact combination in mixed farming, income can be increased, e.g., the number of animals can be increased (as per the food/crop available) to enhance milk production.

Question 2
Give the merits and demerits of fish culture. [NCERT Exemplar]
Answer:
Demerits:

• Threat to biodiversity,
• only economically important and valued fishes will be cultured.

Merits:

• Large amount of desired fishes can be obtained in small area,
• Increased quality of food as fishes are cheaper source of protein.

Question 3
Discuss why pesticides are used in very accurate concentration and in very appropriate manner. [NCERT Exemplar]
Answer:
Pesticides are used in very accurate concentration and in a very appropriate manner because if used in excess it

• harms the soil and causes loss of fertility,
• checks the replenishment of organic matter,
• kills the microorganism of soil,
• causes air, water and soil pollution.

Question 4
(a) Give any three preventive measures for pest control.
(b) What preventive and control measures are used before grains are stored for future use?
Answer:
(a) The three important preventive measures for pest control are:

• Employing crop rotation.
• Use of pest-resistant varieties.
• Employing optimum time of sowing the crops.

(b) Preventive and control measures are used before grains are stored for future use, which include strict cleaning of the produce before storage, proper drying of the produce first in sunlight and then in shade, and fumigations by using chemicals that kill pests.

Question 5
Why is crop variety improvement important in cultivation? Describe the important factors for which variety improvement is done.
Answer:
As we know, weather conditions, soil quality and availability of water are the main factors on which crop yield depends. As weather conditions like drought and flood situation are unpredictable, it is important to have varieties that can grow in adverse climatic conditions. In the same way, varieties that are tolerant to high soil salinity have also been developed. Some of the factors for which crop variety improvement is done are as follows:

• High Yield: To increase the productivity of the crop per acre.
• Improve Quality: Quality considerations of crop products vary from crop to crop. For instance,
  baking quality is important in wheat, protein quality in pulses; oil quality in oilseeds and preserving quality in fruits and vegetables.
• Biotic and Abiotic Resistance: Crop production can fall due to biotic and abiotic stresses under different situations. Thus, varieties resistant to these stresses can improve crop production.
• Change in Maturity Duration: The shorter the duration of the crop from sowing to harvesting, more economical is the variety. It reduces the cost of crop production and allows the farmers to grow multiple crops in a year.
• Wider Adaptability: Developing varieties for wider adaptability helps in stabilising the crop production under different environmental conditions. Also, one variety can then be grown under different climatic conditions in different areas.
• Desirable Agronomic Characteristics: Height and profuse branching are desirable characteristics for fodder crops. Dwarfness is desired in cereals such that fewer nutrients are consumed by these crops. Thus, developing varieties of desired agronomic characters also help in higher yield.

Question .6
Describe the main irrigation systems that are adopted in India.
Answer:
Different kinds of irrigation systems are adopted to supply water to agricultural lands depending on the kinds of water resources available. These include wells, canals, rivers and tanks.

• Wells: They are of two types—dug wells and tube wells. In dug wells, water is collected from water bearing strata while in tube wells water is tapped from the deeper strata. From these wells, water is lifted by pumps for irrigation.
• Canals: Canal system is usually an elaborate and extensive irrigation system. Canals receive water from one or more reservoirs or from rivers. The main canal is divided into branch canals having further distributaries to irrigate fields.
• River lift systems: In this system, water is directly drawn from the rivers for supplementing irrigation in areas lying close to rivers. This system is used in areas where canal flow is insufficient or irregular due to inadequate reservoir release.
• Tanks: Tanks are small storage reservoirs, which intercept and store the run-off of smaller catchment areas.
  Apart from the above systems, some new initiatives have been undertaken for increasing the water available for agriculture. These include rainwater harvesting system and watershed management system. This involves building small check-dams which lead to an increase in groundwater levels. These check-dams stop the rainwater from flowing away and also reduce soil erosion.

Question 7
Enlist the criteria for the selection of crops for mixed cropping.
Answer:
Mixed cropping is employed to minimise risk and as an insurance against crop failure due to abnormal weather conditions. The main criteria’s for selection of the crops for mixed cropping are as follows:

• Duration of Crops: One of the crops should be a long duration and other should be a short duration crop.
• Growth Habit: One of the crops should be growing tall and the other should be growing short. The component crops should have different canopy (i.e., the structure of leaves, stem and flowers found above the ground).
• Nutrient Demand: One of the component crops should require lesser nutrients than the other crop.
• Root Pattern: One of the crop should be deep-rooted while the other should be shallow-rooted.
• Water Requirement: One of the component crops should require lesser water than the other.

Question 8
What are weeds? Enlist the methods employed to control weeds.
Or
Discuss various methods for weed control. [NCERT Exemplar]
Answer:
The unwanted plants in a cultivated field are called weeds. They compete for food, space and light with the main crop plants. They germinate and grow faster, and thus effect the quality and yield of the crop. For these reasons, weed plants need to be removed from the cultivated field in early stage of crop. The methods employed for weed control are as follows:

• Mechanical Method: The weed plants are removed from the field either manually or with the help of agricultural implements like uprooting or hand hoeing or weeding with khurpi, ploughing, etc.
• Cultural Method: This method includes:
  • Proper seed bed preparation
  • Timely sowing of crops
  • Intercropping
  • Crop rotation
• Chemical Methods: By Spraying chemicals that do not harm crop plants but destroy only the weed plants, the latter can be controlled. These chemicals are called weeclicides, e.g., 2, 4-D and atrazine.
• Biological Method: As we know, some insects feed an particular weeds. Thus, we use these insects as biological weed-controlling agents like the use of cochineal insect to control Opuntia weed and the use of the grass carp fish to control aquatic weeds.

Question 9
Differentiate between fertilisers and manures.
Answer:
Differences between fertilisers and manures:

Question 10
How is intercropping different from mixed cropping?
Answer:

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Question.1 List any three human activities that you think would lead to air pollution. ]SAII – 2013]
Answer. Human activities that would lead to air pollution are :

1. Excessive use and burning of fossil fuels like coal and petroleum produces different oxides of nitnopfrand sulphur. These are not only dangerous to our respiratory system but also leads to acid rain.
2. Incomplete combustion of various fuels forms unburnt carbon particles which lowers the visibility, especially in cold weather when water also condenses out of air. This is known as smog and is a visible indication of air pollution.
3. Large usage of automobiles and improperly tuning of engines leads to the formation of carbon monoxide gas and other oxides of nitrogen which causes lot of respiratory problems.
4. Forest fires, excessive mining and ore refining, excessive use of chlorofluorocarbons and v excessive industrialization leads to air pollution.

Question.2 Why do organisms need water ? [SAII-2012]
Answer. Organisms need water due to the following reasons :

1. All cellular processes take place in a water medium.
2. All the reactions that take place’Within our body and within the cells occur between substances that are dissolved in water.
3. Substances are also transported from one part of the body to the other in a dissolved form.
4. Water makes-up about 70% of body weight of all living organisms.
5. It helps in the digestion of food and absorption of nutrients in the blood. Hence, organisms need to maintain the level of water within their bodies in order to stay alive.
6. It helps in maintaining body temperature. –

Question.3 Do you know any activity which may be polluting these water sources ?
Answer.There are many activities which cause pollution of water sources such as :

1. Dumping of waste from factories, sewage from our towns and cities into rivers or lakes.
2.  Discharging hot water from cooling towers into the water bodies affects the breeding capacity of aquatic organisms.

Question.4 How is soil formed ? [SAII – 2013, 2014]
Answer. Over long periods of time, thousands and millions of years, the rocks at or near the surface of the Earth are broken down by various physical, chemical and some biological processes. The end product of this breaking down is the fine particles of soil. There are many other factors which play a vital role in the formation of soil. These factors are :

1. The Sun : It causes heating of rocks which causes cracking and ultimately breaking-up into smaller pieces.
2. Water : It breaks rocks both by freezing and fast flow.
3. Wind : It causes erosion of rocks similar to as done by fast flowing water. It also carries sand from one place to the other like water does.
4. Living organisms : Lichens and moss plants grow on the rock surface and cause rock surface to powder down and form a thin layer of soil. The roots of big trees sometimes go into cracks in the rocks and as the roots grow bigger, the crack is forced bigger.

Question.5 What are the different states in which water is found during the water cycle ? [SAII – 2011]
Answer. Three different states of water can be seen during the water cycle. These states are :

1. Gaseous stateTtn the form of water vapour which evaporates from the surface water).
2. Liquid state (It is formed by the condensation of water vapour and can be seen in the form of rain).
   (iii) Solid state (It is formed by the freezing of liquid droplets in the upper layer of atmosphere which can be seen in the form of snow, hail or sleet).

Question.6 List any three human activities which would lead to an increase in the carbon dioxide content of air. [SAII – 2011]
Answer.Three human activities which would lead to an increase in the CO₂ content of air are :

1. Respiration : It is the natural process of release of CO₂  by both plants and animals. But this release is neither dangerous nor it has any adverse effect on our environment.
2. Combustion of fuels : The various types of fuels are burnt to provide energy for various – , needs like heating, cooking, transportation and industrial fuels.
3. Deforestation : Trees help in the conversion of CO₂  into organic compounds such as glucose, starch etc., by the process of photosynthesis. When these trees are cut non- judiciously, then the level CO₂  increases in our environment.

Question.7 How does nitrogen fixation take place during lightning ? How do plants make use of the nitrates and nitrites present in soil ? [SAII -2014]
Answer.

Nitrogen fixing bacteria mostly found in the root nodules of leguminous plants convert
atmospheric nitrogen molecules into nitrates.
During lightning, the high temperatures and pressure created in the air convert nitrogen into
oxides of nitrogen. These oxides dissolve in water to give nitrous and nitric acids that fall on
land along with rain.

•  Nitrogen fixing bacteria which are found in the roots of leguminous plants convert atmospheric nitrogen into  nitrate (the usable form by plants).
•  During lightning and thunder, the high temperature and pressure help to convert atmospheric nitrogen into  oxides of nitrogen and to give nitric and nitrous acids which fall along with rain.
•  The plants use nitrogen in the form of nitrates and nitrites to form amino acids and
  proteins.
•  The plants are used as food by animals.
•  After the death of plants and animals, the bacteria convert these compounds of nitrogen into nitrates and  nitrites, which are used by new plants to grow.
•  Some other types of bacteria convert nitrites and nitrates into molecular nitrogen, which escapes into  atmosphere and becomes a part of it.

Question.8 Draw labelled diagrams of :
(a) Carbon cycle
(b) Oxygen cycle and briefly explain oxygen cycle.[SAII – 2013]
Answer. (a)

(b)

Oxygen cycle:

•  Oxygen from the atmosphere is used up in combustion, respiration and
  in the formation, of oxides of nitrogen.
•  Oxygen is returned to the atmosphere through photosynthesis. This
  constitutes oxygen cycle in nature.

Question.9 What are the methods of preventing or reducing soil erosion ? [SAII -2012]
Answer. The methods of preventing soil erosion are :
(i) Afforestation : Forests reduce erosion as the roots of trees hold the soil in place.
(ii) Shelter belts : Trees planted in lines or hedges around farmland reduce erosion by
reducing the speed of the wind.
(iii) Contour ploughing : Farmers plough land so that furrows lie across the natural slope of
the land. These furrows trap water and do not allow it to flow down carrying the topsoil.
(iv) Terrace (or step) farming : A terraced hillside is less likely to tie eroded than a natural
hillside. Here a series of steps formed by horizontal strips supported by walls, catch the
descending water. It gives the water sufficient time to percolate Into the soil and nourish
the crop.
(v) Soil cover : Soil left bare after harvesting a crop is often covered with dried vegetation to prevent erosion. Steep slopes that cannot be ploughed are covered with grass or pasture crops.
(vi) Preventing overgrazing : As the grass has a tendency to bind soil molecules, so even a very little grass on a field prevents erosion of soil. But if the grass is overgrazed, it exposes the soil to erosion.

Question.10 Why is the atmosphere essential for life ? [SAII-2011]
Answer. Atmosphere is essential for life because of the following reasons :
(i) It keeps the average temperature of the earth fairly steady during the day and even during the course of the whole year.
(ii) It prevents the sudden increase in temperature during the daylight hours.
(iii) It contains all the important gases which are required for sustaining life on earth. These gases are :
(a) Oxygen for respiration of living organisms and oxidation.
(b) Carbon dioxide for photosynthesis in plants and for making food.
(c) Nitrogen foTproviding inert atmosphere and making proteins.
(iv) The stratosphere region (16-23 km from the surface of Earth) of atmosphere contains a thick layer of ozone which filters the harmful UV radiation from Sun. If these radiations reach on the surface of Earth, then they may cause cancer in animals and are also harmful for plants.

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Question.1
(i) What are the various ways to prevent the diseases ?
(ii) What is immunisation ?
Answer.
(i) We can prevent disease in two ways :
(a) General ways: By preventing exposure to infectious microbes.

•  By providing safe drinking water and public hygiene.
•  By providing proper and balanced diet, (any two)

(b) Specific ways : By immunisation.
(ii)Immunisation : The process of developing immune power in the body to fight against the diseases is called immunisation. In the process of immunisation, a vaccine is introduced into the body doe to which the immune power of the body improves.

Question.2 State two principles of treatment of a disease.
Answer. There are two ways to treat an infectious disease :
(i) By reducing the effect of the disease
(a) By symptomatic treatment. (b) By taking a bed rest
(ii) By killing the microorganisms that act as infectious agents.

Question.3 List any three reasons why you would think that you are sick and ought to see a doctor. If only one of these symptoms were present, would you still go to the doctor ? Why or why not ?
Answer. When there is a disease, either the functioning or the appearance of one or more systems of the body will change for the worse. These changes give rise to symptoms and signs of disease. Symptoms of disease indicate that a person is not well. These symptoms can be in the form of headache, cough, loose motions or wound with pus. These symptoms indicate that there-may be a disease but they do not indicate what the disease is. Therefore, even if you have any of these symptoms, it is advisable to go to the doctor because only he can diagnose about any signs of a disease on the basis of these symptoms. These signs will give a little more definite indication of the presence of a particular disease. But if there is only one symptom of headache, then there is no need of visiting a doctor because it could be due to Tiredness or Stress.

Question .4 What are the different means by which infectious diseases are spread ? [SAII – 2011, 2013]
Answer. The various means by which the infectious diseases get spread are :

1. Through air : This occurs through the little droplets thrown out by an infected person who sneezes or coughs. Someone standing closeby can breathe in these droplets and the microbes get a chance to start a new infection. Examples of such diseases which spread through the air are the common cold, pneumonia and tuberculosis.
2.  Through water: This occurs if the excreta from someone suffering from an infectious gut disease, such as cholera, get mixed with the drinking water used by people living nearby.
   The cholera-causing microbes will enter new hosts through the water they drink and cause disease in them. Such diseases are much more likely to spread in the absence of safe supplies of drinking water.
3. Through sexual contact: Microbial diseases such as Syphilis or AIDS are transmitted by sexual contact from one partner to the other. Other than the sexual contact, the AIDS virus can also spread through blood-to-blood contact with infected people or from an infected mother to her baby during pregnancy or through breast feeding.
4. Through vectors: There are certain animals which carry the infecting agents from a sick person to another potential host. These animals are thus the intermediaries and are called vectors. The commonest vectors are the mosquitoes which spread malaria. In many species of mosquitoes, the females anopheles need highly nutritious food in the form of blood in order to be able to lay mature eggs:

Question. 5 How many times did you fall ill in the last one year ? What were the illnesses ? (a) Think of one change you could make in your habits in order to avoid any/most of the above illnesses.
(b) Think of one change you would wish for in your surroundings in order to avoid any/most of the above illnesses.
Answer. I fell ill thrice in the last one year. At first time, I suffered from common cold, at second time I suffered from influenza (eye-flu) and at third time, I suffered from diarrhoea.
(a) The change which I brought in my habits to avoid any of this type of illness in near future is:
(i) To remain away from people suffering from common cold or eye-flu.
(ii) To clean hands before meals and to take purified drinking water.
(b) Availability of purified drinking water all the time throughout the year.

Question.6 A doctor/nurse/health-worker is exposed to more sick people than others in the community.
Find out how she/he avoids getting sick herself/himself.
Answer. A doctor/nurse/health-worker take the following precautions to avoid getting sick herself. He/She:

1. always wear masks while diagnosing mouth or chest infections.
2. always wear hand gloves even while doing minor surgeries.
3. always clean hands as well as instruments after diagnosis of the patient.
4. makes sure that they are immunized against all contagious diseases.
5. takes balanced diet (especially rich in proteins) to build their powerful immune system.
6. dispose of any sputum, blood sample, urine or stool, properly.

Question.7 Under which of the following conditions is a person most likely to fall sick ?
(a) When she is recovering from malaria.
(b) When she has recovered from malaria and is taking care of someone suffering from
chickenpox.
(c) When she is on a four-day fast after recovering from malaria and is taking care of someone suffering from chickenpox. Why ?
Answer. A person is most likely to fall sick when she is on a four-day fast after recovering from malaria and is taking care of someone suffering from chickenpox. There are following reasons for this :

1. When a person gets a disease like malaria he has loss of appetite, vomiting and high fever. This leads to loss of body fluids and makes body very weak. Under such circumstances if she is on a four day fast, then her defense system will be totally weak and she can even collapse.
2.  With the weak immune system if she is taking care of someone suffering from chickenpox, then it is more likely that she may also get the disease.

Question.8
(a) What is immunisation ?
(b) Define immunity and vaccination.
(c) Define vaccine. .
(d) What type of diseases can be prevented through vaccination ? [SAII -2013]
Answer.
(a) Immunisation is a process of inoculation (injecting) of substance (vaccine) into a healthy person in order to develop immunity against the disease.
(b) Immunity is the ability of a body to recognise, destroy and eliminate external disease-causing agents. This immunisation is done by giving vaccine and thus it is also known as vaccination.
(c) The vaccine is a solution containing the disease-causing organisms in a diluted or weakened form. It may have organisms in living or even dead form.This does not actually cause the disease but this would prevent any subsequent exposure to the infecting microbe from turning into actual disease.
(d) Protection against diseases like smallpox, rabies, polio, diphtheria, chickenpox and hepatitis is provided through vaccination. It has been possible to eradicate smallpox from all regions of the world through a massive vaccination programme.

Question.9 Conduct a survey in your neighbourhood to find out what the three most common diseases are. Suggest three steps that could be taken by your local authorities to bring down the incidence of these diseases.
Answer. After conducting a survey, I have found the following three most common diseases in my locality.
Place of study : Jalandhar (Punjab- India)

Question.10 A baby is not able to tell her / his caretakers that she / he is sick. What would help us to find out:
(a) that the baby is sick ?
(b) what is the sickness ?
Answer.
(a) The following symptoms will help us to find out that the baby is sick :
(i) Repeated crying and not responding to any stimuli.
(ii) High body temperature.
(iii) Loose motions.
(iv)Drooping of eyes.
(v) Redness of eyes.
(b) The following signs will help us to find out what is the sickness :
(i) Yellowing of eyes, pale skin and passing of yellow urine indicate that baby is suffering from jaundice.
(ii) Redness in the eye and persistent rubbing of eyes indicate about eye-flu.
(iii) Gripping pain in the stomach, loose skin and repeated loose motions indicates about diarrhoea.
(iV) High fever, headache, nausea, muscular pains and feeling very cold and shivering indicates about malaria.
(v) If only fever is there with no other visible symptoms then laboratory tests are to be done which will reveal about the signs of any disease.

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Question.1 Distinguish between transverse and longitudinal waves. (Three points) [SAII-2014]
Answer.
Transverse waves
(a) Particles the medium vibrate at right angles.
(b) Alt. crests and troughs formed.
(c) e.g., water wavesv
Longitudinal waves
(a) Particles vibrate parallel to the direction of waves.
(b) Alt. compressions, rarefaction formed.
(c) e.g., sound waves.

Question.2 State three characteristics of a musical sound. On what factors do they depend. [SAII-2014]
Answer.
Characteristics of musical sound are:

•  Loudness-Amplitude affect loudness-more amplitude loud/Less amplitude soft sound.
•  Pitch-frequency affects pitch-more frequency more pitch, Less freq. less pitch.
•  Quality or Timhpr.

Question.3 A stone js dropped into a well 44 m deep and the sound of splash is heard after 3.12 sec. Find the speed of sound in air. [SAII-2014]
Answer.

Question.4
(a) The sound of which of the following frequencies are audible to human ears : 2 Hz, 5 Hz, . 20 Hz, 200 Hz, 2000 Hz.
(b) How [paths of, certain families are able to escape capture ? [SAII-2014]
Answer.
(a) 20 Hz, 200 Hz and 2000 Hz.
(b) They do not reflect the ultrasounds sent towards them by bats.

Question.5 How does the sound produced by a musical instrument, reach your ears? Astronauts need radio transmitter to talk to each other on moon. Why ? [SAII-2014]
Answer. The sound produced by the musical instrument makes the molecules of air vibrate. These vibrations are carried forward by the other molecules till they reach our ear. These then vibrate our eardrum to produce sound. Since sound requires a medium to propagate, therefore, sound cannot travel between astronauts on the moon, hence they use radio transmitters.

Question.6 How does the sound produced by a vibrating object in a medium reach your ear?
Answer. Air is the commonest material through which sound propagates. When vibrating objects, like prongs of a tuning fork move forward, they push the molecules of the air in front of them. This in turn compresses the air, thus, creating a region of high pressure and high density called compression. This compression in the air travels forward. When the prongs of the tuning fork move backward, they create a region of low pressure in the air, commonly called rarefaction. This region has low pressure, low density and more volume. As the tuning fork continues to vibrate, the regions of compression in the air alternate with the regions of rarefaction. These regions alternate at the same place. The energy of vibrating tuning fork travels outward. This energy which reaches the ears, makes the eardrums to vibrate and thus we hear sound.

Question.7 What are wavelength, frequency, time period and amplitude of a sound wave? [SAII-2013]
Answer. Wavelength: It is the linear distance between two consecutive compressions or two consecutive rarefactions.
Frequency: The number of compressions or rarefactions taken together passing through a point in one second is called frequency.
Time period : It is the time taken by two consecutive compressions or rarefactions to cross a point.
Amplitude: It is the magnitude of maximum displacement of a vibrating particle about its mean position.

Question.8 Does sound follow the same laws of reflection as light does? Explain. [SAII-2010]
Answer. Yes, sound and light follow the same laws of reflection given below :
(a) Angle of incidence at the point of incidence = Angle of reflection.
(b) At the point of incidence, the incident sound wave, the normal and the reflected sound wave lie in the same plane.

Question.9 Explain the working and application of SONAR ?
Answer. SONAR is a device for determining water depth and locating underwater objects like reefs, submarines and schools of fish. To find the depth of an ocean, a strong ultrasonic wave is sent from the ship towards the bottom of ocean.
On striking the bottom of the ocean, the ultrasonic wave is reflected upward toward the ship. This wave is received by a suitable receiver. The time of travel from the source of sound to the receiver is noted. We can calculate the depth of ocean floor if the velocity of sound in water is known :
Depth of ocean floor = v x t/2

Question.10 With the help of a labelled diagram show that sound needs a material medium for its propagation.
Answer. A well labelled diagram is as shown: Take an electric circuit which consists of a cell, a switch and an electric bell arranged inside a bell jar, which stands on the platform of an evacuating pump.
The switch Of the bell is pressed to close the electric circuit. When there is air within the bell jar, sound is heard. Air is now pumped out of the bell jar. When the air is completely removed from the bell jar, no sound is heard as it is obvious from fig. because the medium of air which has to carry energy from the bell to the bell jar is removed. It shows that sound needs material medium for its propagation.

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Q.1 What is meant by mechanical energy ? State its two forms. State the law of conservation of energy. Give an example in which we observe a continuous change of one form of energy into another and vice-versa.
(b) Calculate the amount of work required to stop a car of 1000 kg moving with a speed of 72 km h”1. [SAII-2013]
Answer.
(a) It is the sum of KE and PE of an object. It states that energy can neither be created nor be destroyed. We observe a continuous change in energy in a simple pendulum and its : explanation. At the mean position, the energy is wholly kinetic while at the extreme position it is wholly potential. As the pendulum oscillates its energy continuously changes between kinetic and potential.

Q.2 (a)Derive an expression for kinetic energy of a body having mass m and moving with a velocity v.
(b)When velocity of a body is increased 5 times, what is the change in its kinetic energy ?
(c)Two masses m and 2m are dropped from heights h and 2h. On reaching the ground, which will have greater kinetic energy and why ? [SAII-2013]
Answer.
(a)For derivation see above questions.
(b)Kinetic energy is given by the expression
KE = 1/2 mv², therefore, if velocity is made 5 times KE will increase by 25 times.
(c)More the potential energy more will be the kinetic energy of the body when it falls. Hence, the body with mass 2m will have greater kinetic energy as it has more potential energy.

Question.3
(a)State the law of conservation of energy.
(b)What is the work done to increase the velocity of a car from 36 km h-1 to 72 km h~1 if the mass of the car is 1500 kg ? Does the work done by the force have a negative or a positive magnitude ?
(c)Where does an oscillating pendulum have maximum PE and KE ? [SAII-2013]
Answer.

Q.4 (a) Define power. Give its SI unit.
(b) Taking the example of a simple pendulum, explain the variations in the forms of energy and the; inter-conversions involved. [SA II-2011]
Answer.
(a) Power is defined as the rate of doing work. Its SI unit is watt.
(b) For a simple pendulum, the inter-conversion of energy is as shown in the table below :

Q.5 (a)What is the commercial unit of energy ? Give its relationship with SI unit of energy.
(b)An electric bulb of 60 W is lighted for 10 hours everyday. How many units of electrical energy is consumed by this bulb in one day ? [SAII-2013]
Answer.

Question.6 Define : (a) power (b) work done (c) kinetic energy. Give SI unit of each. [SAII-2014]
Answer.
(a) The rate of doing work is called power. Its SI unit is watt.
(b) Work is the product of force and displacement. Its SI unit is joule.
(c) It is the energy possessed by a body by virtue of its motion. Its SI unit is joule.

Question.7 The kinetic energy of an object of mass ‘m’ moving with a velocity of 5 ms-1 is 25 J. What will be its kinetic energy when its velocity is doubled? What will be its kinetic energy when its velocity is increased three times?
Solution.

Question.8 Certain force acting on a 20 kg mass changes its velocity from 5 ms^-1 to 2 ms^-1. Calculate the work done by the force. [SAII-2013]
Solution.

Question.9 A body of mass 4 kg initially at rest is subjected to a force of I6 N. What is the kinetic energy acquired by the body at the end of 10 s? [SAII-2010]
Solution.

Question 10.A mass of 10 kg is dropped from a height of 50 cm. Find its : (i) Kinetic energy (ii) Velocity just as it reaches the ground. Does the velocity depend upon the mass of the particle? Explain. [Take g = 10 ms^-2] [SAll-2012]
Solution.

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Q 1. Name the three sub-atomic particles of an atom.
Answer: The sub-atomic particles of an atom are

Q 2. Helium atom has an atomic mass of 4 u and two protons in its nucleus. How many neutrons does it have?
Answer:

Q 3. How will you find the valency of chlorine, sulphur and magnesium?
Answer:

Q4. Compare all the proposed Bohr’s models of an atom given in this chapter.
Answer:

Q 5. Explain with examples:
(i) Atomic number (ii) Mass number,
(iii) Isotopes and (iv) Isobars.
Give any two uses of isotopes.
Answer: (i) Atomic number: The atomic number of an element is equal to the number of protons in the nucleus of its atom. e.g., Oxygen has 6 protons hence atomic no. = 6.
(ii) Mass number: The mass number of an atom is equal to the number of protons and neutrons in its nucleus.
Nucleons = number of protons + number of neutrons Example: Protons + Neutrons = Nucleus = Mass number  6 + 6 = 12

(iii) Isotopes: Isotopes are atoms of the same element which have different mass number but same atomic number.

(iv) Isobars: Isobars are atoms having the same mass number but different atomic numbers.

Both calcium and argon have same mass number but different atomic number.
Two uses of isotopes are:
(i) An isotope of iodine is used in the treatment of goitre.
(ii) An isotope of uranium is used as a fuel in nuclear reactors.

Q 6. Na⁺ has completely filled K and L shells. Explain.
Answer: Sodium atom (Na), has atomic number =11
Number of protons =11
Number of electrons = 11
Electronic configuration of Na = K L M – 2 8 1
Sodium atom (Na) looses 1 electron to become stable and form Na⁺ ion. Hence it has completely filled K and L shells.

 The average atomic mass of a sample of an element X is 16.2 u. What are the percentages of isotopes ¹⁶₈X and ¹⁸₈X in the sample?
Answer: Let the percentage of ¹⁶₈X be x and the percentage of ¹⁶₈X be 100 – x.

Q 7. Complete the following table.

Answer:

Q 8. Write the electronic configuration of any one pair of isotopes and isobar.
Answer. Isotopes: Atoms of same element having same atomic number but different mass number.

Q 9. What are canal rays?
Answer: Canal rays are positively charged radiations which led to the discovery of positively charged sub-atomic particle called proton.

 Q.10 What do you think would be the observation if the a-particle scattering experiment is carried out using a foil of a metal other than gold?
Answer: On using any metal foil, the observations of the a-particle scattering experiment would remain the same as all atoms would have same structure.

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Q.1 Why are xylem and phloem called complex tissues? How are they different from one other ? [NCERT Exemplar]
Answer:
Xylem and phloem are called as complex tissues as they are made up of more than one type of cells. Following are the differences between xylem and phloem:

Xylem	Phloem
1. Xylem mainly consists of dead cells (except xylem parenchyma).	1. Phloem consists of living cells (except phloem fibre).
2. It conducts water and minerals from roots to aerial parts of the plant.	2. It translocates prepared food from leaves to storage organs and growing parts of the body.

Q.2

Why are plants and animals made of different types of tissue?
Answer:
Plants and animals are two different types of organisms. Plants are autotrophic organisms, so they prepare their own food by photosynthesis. Moreover, plants are stationary or fixed organisms. Since they do not consume or need much energy, so most of the tissues of plants are supportive. Most of these tissues such as xylem, phloem, sclerenchyma and cork are dead tissues, i.e., they do not contain living protoplasm.

Animals on the other hand, are heterotrophic organisms. They have to move in search of food, mate and shelter; so they need more energy as compared to plants. Most of these tissues contain living protoplasm.
There are some tissues in plants which divide throughout life. They divide for the growth and reproduction of the plants. In contrast to plants, growth in animals is uniform.

Q.3
Differentiate between parenchyma and collenchyma.
Answer:

Q.4
Differentiate between collenchyma and sclerenchyma.
Answer:

Q.5
What is a neuron? Write the structure and functions of a neuron.
Answer:
Nervous tissue contains highly specialised unit cells called nerve cells or neurons. Each neuron has the following three parts:

• The cyton or cell body: It contains a central nucleus and cytoplasm with characteristic deeply stained particles, called Nissl granules.
• The dendrites: These are short processes arising from the cyton.
• The axon: It is a single, long, cylindrical process of uniform diameter It carries impulses away from the cell body.

Functions:
Neurons have the ability to receive stimuli from within or outside the body and conduct impulses to different parts of the body. The impulses travel from one neuron to another neuron and finally to the brain or spinal cord.

Q.6
Differentiate between meristematic tissue and permanent tissue.
Answer:

Q. 7
Briefly describe striated and smooth muscles with their functions.
Answer:
The striated muscle fibres are long or elongated, non-tapering, cylindrical and unbranched. These cells have a number of nuclei called sarcolemma.These muscle fibres shows alternate dark and light stripes or striations and so they are called as striated muscles. These muscles occur in muscles of limbs, body wall, face, neck, etc.
Functions of striated muscles:

• Striated muscles are powerful and undergo rapid contraction and expansion.
• Striated muscles provide the force for locomotion and all other voluntary movements of the body.

The smooth muscles are also known as unstriated or involuntary muscles. Smooth muscles occur as bundles or sheets of elongated fusiform or spindle-shaped cells or fibres. They are held together by loose connective tissue. These muscle fibres are uninucleate and do not bear any bands, stripes or striation across them.

These muscles are found in the walls of the alimentary canal and internal organs, ducts of glands and blood vessels. Smooth muscles are also found in the stomach, intestine, ureters, bronchi, iris of the eye, etc.
Functions of smooth muscles:

• Smooth muscles do not work according to our will, so they are also called involuntary muscles. Movement of food in the alimentary canal or the contraction and relaxation of blood vessels are involuntary movements.
• Smooth muscles contract slowly but can remain contracted for a long period of time. Due to this characteristic, the food passes to the next step of digestion in the alimentary canal.

Q.8
Describe the types of connective tissues along with their functions.
Answer:
There are five types of connective tissues:
(i) Areolar connective tissue: It is a loose and cellular connective tissue. It joins skin to muscles, fills spaces inside organs, and is found around muscles, blood vessels and nerves.
Functions:

• It acts as a supporting and packing tissue between organs lying in the body cavity.
• It helps in repair of tissues after an injury.
• It also helps in combating foreign toxins.
• It fixes skin to underlying muscles.

(ii) Dense regular connective tissue: It is a fibrous connective tissue, characterised by ordered and densely packed collection of fibres and cells. Dense regular connective tissue is the principal component of tendons and ligaments.
Functions:

• Tendons: Tendons are cord-like, strong, inelastic structures that join skeletal muscles to bones.
• Ligament: They are an elastic structure which connects bones to bones.

(iii) Adipose tissue: Adipose tissue is basically an aggregation of fat cells. The adipose tissue is abundant below the skin, between the internal organs and in the yellow bone marrow.
Functions:

• It serves as a fat reservoir.
• It provides shape to the limbs and the body.
• It keeps visceral organs in position.
• It forms shock-absorbing cushions around kidneys and eyeballs.
• It acts as an insulator. Being a poor conductor of heat, it reduces heat loss from body, i.e., it regulates body temperature.

(iv) Skeletal tissue: The skeletal or supporting tissue includes bone and cartilage which form the endoskeleton of vertebrate body.

• Cartilage: The cartilage is a specialised connective tissue which is compact and less vascular. Cartilage can be found in ear pinna, nose tip, epiglottis, intervertebral discs, end of long bones, lower ends of ribs and rings of trachea.
• Bone: Bone is a strong and non-flexible tissue. Like cartilage, bone is also a specialised connective tissue.

Functions:

• Cartilage provides support and flexibility to the body parts. It smoothens the surface at joints.
• Bone provides shape and skeletal support to body.
• Bone protects vital body organs such as brain, lungs, etc.
• Bone anchors the muscles.

(v) Fluid connective tissue: Fluid connective tissue links the different parts of the body and maintains continuity in the body. It includes blood and lymph.

• Blood: In this tissue, cells move in a fluid or liquid matrix or medium called blood plasma. Blood occurs in blood vessels called arteries, veins, and capillaries which are connected together to form the circulatory system.
• Lymph: Lymph is a colourless fluid that has been filtered out of the blood capillaries.

Functions:

• Blood transports nutrients, hormones and vitamins to the tissues and transports excretory products from the tissues to the liver and kidney.
• Lymph transports the nutrients (oxygen, glucose) that may have filtered out of the blood capillaries back into the heart to be recirculated in the body.
• Lymph brings C02 and nitrogenous wastes from tissues to the blood.

Q.9
Differentiate between sclerenchyma and parenchyma tissues. Draw well labelled diagram. [NCERT Exemplar]
Answer:

Q.10
Describe the structure and function of different types of epithelial tissues. Draw the diagram for each type of epithelial tissue. [NCERT Exemplar]
Answer:
Epithelial tissues are of following types:
(a) Simple squamous epithelium
(b) Stratified squamous epithelium
(c) Columnar epithelium
(d) Cuboidal epithelium

(a) Simple squamous epithelium: They are present in cells lining blood vessels or lung alveoli where transportation of substances occurs through a selectively permeable surface, there is a simple flat kind of epithelium.

(b) Stratified squamous epithelium: Skin epithelial cells are arranged in many layers to prevent wear and tear. Since, they are arranged in a pattern of layers, the epithelium is called stratified squamous epithelium.

(c) Columnar epithelium: Where absorption and secretion occur, as in the inner lining of the intestine, these tall epithelial cells are present. This columnar epithelial facilitates movement across the epithelial barrier. In the respiratory tract, the columnar epithelial tissue also has cilia, which are hair-like projections on the outer surfaces of epithelial cells. These cilia can move and their movement pushes the mucus forward to clear it. This type of epithelium is thus ciliated columnar epithelium.

(d) Cuboidal epithelium: These form the lining of the kidney tubules and ducts of salivary glands where these provide mechanical support. Sometimes, a portion of the epithelial tissue folds inward and a multicellular gland is formed. This is glandular epithelium.

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Q.1 Suppose that the radius of the earth becomes twice of its original radius without any change in its mass. Then what will happen to your weight?
Answer:
We know that F = GMmr2 as weight of a body is the force with which a body is attracted towards the earth,
∴ W = GMmr2
If the radius of the earth becomes twice of its original radius, then
W = GMm(2r)2
= GMm4r2=W4
i.e., weight will be reduced to one-fourth of the original.

Question 2.
Prove that if the earth attracts two bodies placed at same distance from the centre of the earth with the same force, then their masses are equal.
Answer:
Let P and Q be the two bodies,
the mass of body P = m₁
And the mass of body Q=m₂
As per the universal law of gravitation, the force of attraction between the earth and the body P is given by,
F_p = G×Me×m1R2 …..(1)
Where, R is the distance of the body from the centre of the earth.
Similarly, the force of attraction between the earth and the body Q is given by
F_Q = G×Me×m2R2 …….(2)
Since, the two forces, i.e., F_p and F_Q are equal, thus from (1) and (2),
G×Me×m1R2=G×Me×m2R2
⇒ m₁ = m₂

Question 3.
Give three differences between acceleration due to gravity (g) and universal gravitational constant (G).
Answer:
Differences between g andG

Acceleration due to gravity (g)	Universal gravitational constant (G)
1.  Acceleration due to gravity is the acceleration acquired by a body due to the earth’s gravitational pull on it.2.    g is a vector quantity.3.   It is different at different places on the surface of the earth. Its value also varies from one celestial body to another.	1. Gravitational constant is numerically equal to the force of attraction between two masses of 1 kg that are separated by a distance of 1 m.2.  G is a scalar quantity.3. The ‘G’ is a universal constant, i.e., its value is the same (i.e. 6.7 × 10-11 Nm2 kg-2) everywhere in the universe.

Question 4.
On the earth, a stone is thrown from a height in a direction parallel to the earth’s surface while another stone is simultaneously dropped from the same height. Which stone would reach the ground first and why? [NCERT Exemplar]
Answer:
For both the stones
Initial velocity, u = 0
Acceleration in downward direction = g

Both stones will take the same time to reach the ground because the two stones fall from the same height.

Question 5.
Calculate the average density of the earth in terms of g, G and R.
Answer:
We know that g = GMR2 or M = gR2G
⇒ Average density of the earth, D =  Mass  Volume =gR2G×Ve
(Where V_e is the volume of the earth)
or D = gR2G43πR3=3g4πGR

Question 6.
Prove that if a body is thrown vertically upward, the time of ascent is equal to the time of descent.
Answer:
Upward motion
v = u + gt₁
0 = u – gt₁
t₁ = ug …(1)
Downward motion
v = u + gt₂
v = 0 + gt₂
As the body falls back to the earth with the same velocity it was thrown vertically upwards.
∴ v = u
u = 0 + gt₂
t₂ = u/g …(2)
From (1) and (2), we get t₁ = t₂
⇒ Time of ascent = Time of descent

Question 7.
Two objects of masses ml and m2 having the same size are dropped simultaneously from heights h₁ and h₂, respectively. Find out the ratio of time they would take in reaching the ground. Will this ratio remain the same if (i) one of the objects is hollow and the other one is solid; and (ii) both of them are hollow, size remaining the same in each case? Give reasons. [NCERT Exemplar]
Answer:
As u = 0, h₁ = 12gt21
h₂ = 12gt22,
ι1t2=h1h2−−√
Ratio will not change in either case because acceleration remains the same. In case of free fall acceleration does not depend upon mass and size.

Question 8
Derive expression for force of attraction between two bodies and then define gravitational constant.
Answer:
“Every body in the universe attracts every other body with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.” Let us consider two bodies A and B of masses m₁ and m₂ which are separated by a distance r. Then the force of gravitation (F) acting on the two bodies is given by
F ∝ m₁ × m₂…(1)
ans F ∝ 1r2 ..(2)
Combining (1) and (2), we get
F ∝ m1×m2r2
or F = G × m1m2r2 ……..(3)
where G is a constant known as universal gravitational constant.
Here, if the masses mx and m2 of the two bodies are of 1 kg and the distance (r) between them is 1 m, then putting m₁ = 1 kg, m₂ = 1 kg and r = 1 m in the above formula, we get
G = F
Thus, the gravitational constant G is numerically equal to the force of gravitation which exists between two bodies of unit masses kept at a unit distance from each other.

Question 9.
Define acceleration due to gravity. Derive an expression for acceleration due to gravity in terms of mass of the earth (M) and universal gravitational constant (G).
Answer:
The acceleration produced in the motion of a body falling under the force of gravity is called acceleration due to gravity. It is denoted by ‘g’.
The force (F) of gravitational attraction on a body of mass m due to earth of mass M and radius R is given by
F = GmMR2 …..(1)
We know from Newton’s second law of motion that the force is the product of mass and acceleration.
∴ F = ma
But the acceleration due to gravity is represented by the symbol g. Therefore, we can write
F = mg …(2)
From the equation (1) and (2), we get
mg = GmMR2 or g = GMR2 …(3)
When body is at a distance V from centre of the earth then g = GMr2

Question 10

From a cliff of 49 m high, a man drops a stone. One second later, he throws another stone. They both hit the ground at the same time. Find out the speed with which he threw the second stone.
Answer:
For the first stone
u = 0 ms^-1, h = 49 m,
As we know s = ut + 12 gt²
∴ 49 = 0 × t + 12 × 9.8 × t²
⇒ t² = 989.8 = 10
⇒ t = 10−−√ = 3.16 s
i.e., First stone would take 3.16 s to reach the ground.
For the second stone,
the time taken by the second stone to reach the ground is one second less than that taken by the first stone as both the stones reach the ground at the same time.
That is, for the second stone, t = (3.16 – 1)s = 2.16s
∴ For the second stone,
g = 9.8 ms^-2, h = 49 m, t = 2.16 s, u = ?

i.e., the second stone was thrown downward with a speed of 12.1 ms^-1.

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Q.1
Which of the following are tri-atomic and tetra-atomic molecules?
CH₃Cl, CaCl₂, NH₃, PCl₃, P₂O₅, H₂O, C₂H₅OH
Answer:
(i) Tri-atomic molecules are CaCl₂, H₂O.
(ii) Tetra-atomic molecules are NH₃, PCl₃.

Q.2
Differentiate between the actual mass of a molecule and gram molecular mass.
Answer:
Actual mass of a molecule is obtained by dividing the molar mass by Avogadro’s number whereas gram molecular mass represents the molecular mass expressed in grams, i.e., it is the mass of 1 mole of molecules, i.e., Avogadro’s number of molecules.

Q.3
Calculate the formula mass of sodium carbonate (Na₂CO₃.10H₂O).
Answer:
Formula mass of sodium carbonate
= (2 × atomic mass of Na) + (1 × atomic mass of C) + (3 × atomic mass of O) + 10 [(2 × atomic mass of H) + (1 × atomic mass of O)]
= 2 × 23 + 1 × 12 + 3 × 16 + 10 [(2 × 1) + (1 × 16)]
= 46 + 12 + 48 + 180 = 286 u

Q.4
Calculate the mass of one atom of hydrogen atom.
Answer:
1 mole of hydrogen atom = 1 g
or 6.022 × 10²³ atoms of hydrogen weigh = 1 g
Mass of one atom = 16.022×1023g
= 1.66058 × 10^-24g

Q.5
How many moles are present in 4 g of sodium hydroxide?
Answer:
Gram molar mass of NaOH = 23 + 16 + 1 = 40 g
40 g of NaOH = 1 mol
∴ lg of NaOH = 140mol
∴ 4 g of NaOH = 140 × 4 mol = 0.1 mol

Q.6
A sample of ammonia weighs 3.00 g. What mass of sulphur trioxide contains the same number of molecules as are in 3.00 g ammonia?
Answer:
Number of moles of ammonia in 3.00 g = 3.0017 mol
= 0.1764 mol
Molecular mass of S0₃ = 1 × 32u + 3 × 16u = 80u
1 mole of SO₃ weighs 80 g
∴ 0.1764 moles weigh = 80 × 0.1764 g
= 14.11 g

Q.7

How many (a) molecules (b) hydrogen atoms (c) oxygen atoms are there in 0.5 mol of water?
Answer:
(a) 1 mol of water contains 6.022 × 10²³ molecules
∴ 0.5 mol of water contains 6.022×10232 molecules
= 3.011 × 10²³ molecules

(b) 1 molecule of water contains 2 atoms of hydrogen
1 mol of water contains 2 × 6.022 × 10²³ atoms of hydrogen
∴ 0.5 mol of water contains 2×6.022×10232 atoms of hydrogen
= 6.022 × 10²³ atoms of hydrogen

(c) 1 molecule of water contains 1 atom of oxygen
1 mol of water contains 6.022 × 10²³ atoms of oxygen
∴ 0.5 mol of water contains 6.022×10232 atoms of oxygen
= 3.011 × 10²³ atoms of oxygen

Q.8
How many atoms would be present in a black dot marked on the paper with graphite pencil as a full stop at the end of a sentence. [Given mass of a dot = 10^-18 g]
Answer:
1 mole of carbon atoms weigh = 12 g
Also, 1 mole of carbon atoms = 6.0 2 2 × 10²³ atoms
Thus, 12 g of carbon atoms has 6.022 × 10²³ atoms.
∴ 10^-18 g of carbon will have 6.022×102312×10−18 × 10^-18 carbon atoms
= 5.02 × 10⁴ carbon atoms.

Q 9
Calculate the number of moles present in:
(i) 3.011 × 10²³ number of oxygen atoms.
(it) 60 g of calcium
[Given that atomic mass of Ca = 40 u, Avogadro No. = 6.022 × 10²³]
Answer:
(i) 1 mole of oxygen contains 6.022 × 10²³ atoms
∴ 6.022 × 10²³ atoms of oxygen = 1 mol
1 atom of oxygen = 16.022×1023 mol
∴ 3.011 × 10²³ atoms of oxygen = 1×3.011×10236.022×1023 mol
= 0.5 mol

(ii) Atomic mass of Ca = 40 u
40g of calcium = 1 mol
60g of calcium = 6040 mol =1.5 mol

Q 10
Calculate the mass per cent of each element of sodium chloride in one mole of it.
Answer:
Molecular mass of NaCl = (1 × 23 + 1 × 35.5) u = 58.5 u
Atomic mass of sodium = 23 u

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