NCERT Exemplar for Class 8 Science Solutions Chapter 18 Pollution of Air and Water

Multiple Choice Questions

1. Air is a mixture of various gases. One of the gases is 21% part of the air and is essential for the survival of human beings. This gas is 

(a) Nitrogen 

(b) Oxygen 

(c) Ozone 

(d) Argon 

Ans: (b) Oxygen is 21% of the total atmosphere, nitrogen is 78.09%, argon is 0.93% and other gases are 0.3%.

2. Which of the following is not a source of air pollution? 

(a) Automobile exhaust 

(b) Burning of firewood 

(c) Windmill 

(d) Power plant 

Ans: (c) The windmills does not liberate any harmful gases and are thus not a source of air pollution. 

3. Boojho wishes to contribute to reducing air pollution. Which vehicle should he use for going to school? 

(a) Car 

(b) School bus 

(c) Auto-rickshaw 

(d) Scooter 

Ans: (b) School bus. This will help to reduce the traffic because this is a public means of transport. 

4. Which of the following is not a way to conserve water? 

(a) Replace 

(b) Reduce 

(c) Reuse 

(d) Recycle 

Ans: (a) Formula “3R” that is “Reduce, reuse and recycle”. These are the finest ways to conserve resources. Replacing the water is not any solution. 

5. The type of pollution which is likely to affect Taj Mahal in Agra to a greater extent is 

(a) Air pollution 

(b) Water pollution 

(c) Soil pollution

(d) Noise pollution 

Ans: (a) Air pollution is harming the Taj Mahal.

6. Incomplete combustion of fuel such as petrol and diesel gives 

(a) Nitrogen oxide 

(b) Sulphur dioxide 

(c) carbon monoxide 

(d) carbon dioxide 

Ans: (c) Carbon monoxide is a very poisonous gas and is produced when the fuel is burnt incompletely. 

7. The phenomenon of marble cancer is due to 

(a) Soot Particles 

(b) CFCs 

(c) Fog 

(d) Acid Rain 

Ans: (d) Acid rain is the product of the reaction of SO2 and NO2 gases with water to form acids like sulphuric and nitric. 

8. Potable water is the water that is 

(a) Obtained from a river. 

(b) Obtained from a lake. 

(c) Pure and fit for drinking. 

(d) Used only for washing clothes. 

Ans: (c) Water that we can drink is known as potable water. 

9. Which of the following procedures will give you water free from all impurities? 

(a) Adding chlorine tablets 

(b) Distillation 

(c) Boiling 

(d) Filtration 

Ans: (b) By the process of distillation, all the impurities of water are removed. 

10. A pond contains clean water. Which of the following activities will produce the least pollution of water? 

(a) Washing clothes in the pond 

(b) Animals bathing in the pond 

(c) Washing motor vehicles in the pond 

(d) Swimming in the pond. 

Ans: (d) Water is least polluted by swimming in the pond as no harmful chemicals are released into it. 

11. Trees help in reducing the pollution of our environment. Lakhs of trees are planted by people in the month of July every year. The occasion is called 

(a) Forest Conservation Day 

(b) Plantation month 

(c) Van Mahotsav

(d) Wildlife week 

Ans: (c) In the month of July every year, “Van Mahotsav” is celebrated. 

12. Which of the following is not a greenhouse gas? 

(a) Nitrogen gas 

(c) Methane gas 

(b) Water vapour 

(d) Carbon dioxide 

Ans: (a) Nitrogen gas is not a greenhouse gas as it does not trap heat and does not contribute to global warming. 

Very Short Answer Questions

13. Name the chemicals which are used in refrigerators and air conditioners and damage the ozone layer when released into the air. 

Ans: Chlorofluorocarbons are the gases used in electric appliances like air conditioners and refrigerators. 

14. Name any two sources which cause air pollution due to suspended particulate matter. 

Ans: The major sources of air pollution are: 

i. Industrial activities. 

ii. Combustion of fuel by Automobiles. 

15. Name two gases that are mainly responsible for acid rain? 

Ans: Sulphur dioxide (SO2) and nitrogen dioxide (NO2) are the two gases that are mainly responsible for causing acid rain. 

16. The quality of air at various locations is monitored regularly by the government and other agencies? In what way can you use these data? 

Ans: We can use this data to spread awareness about the air pollution that results in the poor quality of air around us. 

17. Combustion of fossil fuels generates a lot of air pollution. Can you suggest any two alternative sources of energy which do not cause any pollution? 

Ans: Solar energy and wind energy. These two are sources of energy that does not cause any pollution. 

18. Name any two water pollutants which are toxic for plants and animals. 

Ans: Arsenic and lead are the two toxic water pollutants that are very toxic to plants and animals. They can lead to deformities in the bodies of plants and animals. 

Short Answer Questions

19. A lot of dry leaves are collected in a school garden and are burnt every day. Do you think that it is right to do so? If not, what should be done to dispose of the dry leaves? 

Ans: When we burn the leaves, this causes air pollution. Due to this burning, there are various harmful gases that are released into the atmosphere. As an alternative to burning, we can compose them. In this way, we can get manure. 

20. The level of air pollution is higher at a busy traffic intersection. Why? 

Ans: At busy traffic intersections, many vehicles like cars, buses, scooters and all other automobiles stop throughout the day. Each automobile releases a huge amount of toxic and pollutant gases. The suspended particle matter is suspended in the air around that area that makes it polluted. 

21. Fill in the blanks with the help of words given in brackets after each sentence. 

(a) When air is contaminated by ________ substances which have a ________ effect on both the ________ and ________, it is referred to as ________. (Air pollution, harmful, living, unwanted, non-living, pollutants). 

Ans: Unwanted, harmful, living, non-living, air pollution. 

(b) Many ________ are responsible for causing ________ pollution. Petroleum ________ are a major source of ________ pollutants like ________ and ________. (Sulphur dioxide, refineries, industries, nitrogen dioxide, gaseous, liquid, people, air). 

Ans: Industries, air, refineries, gaseous, sulphur dioxide, nitrogen dioxide. 

(c) While ________ your teeth, leaving the ________ running may waste several ________ of water. (Tap, litres, brushing, washing, drops) 

Ans: Brushing, tap, litres. 

(d) Water which is suitable for _________ is called ________ water. (Washing, bathing, drinking, potable, soft). 

Ans: Drinking, potable 

(e) Water which looks clean still has disease carrying ________ and ________ impurities. (Insects, microorganisms, particles, dissolved, harmful). 

Ans: Microorganisms, dissolved. 

22. Match the following: 

Ans: The answers to Column I are written in front of Column II. 

23. Find out the wrong statements and write them in their correct form. 

(a) We can survive for some time without air but we cannot survive even for a few minutes without food. 

Ans: This statement is incorrect. The correct statement is “We can survive for some time without food but we cannot survive even for a few minutes without air.”

(b) A brick kiln emits a lot of smoke and other harmful gases causing air pollution. 

Ans: This statement is correct. 

(c) Carbon monoxide is produced by the complete burning of fuels such as coal, petrol, and diesel. 

Ans: This statement is incorrect. The correct statement is “Carbon monoxide is produced by incomplete burning of fuels such as coal, petrol, and diesel.”

(d) Chlorination is a commonly used chemical method for killing germs in the water. 

Ans: This statement is correct.

(e) Water that is suitable for drinking is called soft water. 

Ans: This statement is incorrect. The correct statement is “Water that is suitable for drinking is called potable water.”

24. In the following statements, the underlined words are jumbled up. Write them in their correct form. 

(a) Air contains 78% ginroten and 21% gonexy. 

Ans: Air contains 78% Nitrogen and 21% Oxygen. 

(b) Vehicles produce high levels of pollutants like carbon dioxide, nitrogen oxides, nobrac moondexi and mosek. 

Ans: Vehicles produce high levels of pollutants like carbon dioxide, nitrogen oxides, Carbon-monoxide and smoke. 

(c) Carbon dioxide, thaneme, nitrous oxide and water vapour are known as heengrouse sesga.

Ans:  Carbon dioxide, methane, nitrous oxide and water vapour are known as greenhouse gases. 

(d) Gangotri glacier in Himalaya has started melting because of lablog ringwam. 

Ans: Gangotri glacier in Himalaya has started melting because of global warming. 

(e) Whenever harmful substances such as wagese, toxic chemicals, silt, etc. get mixed with water, the water becomes potdulle. 

Ans: Whenever harmful substances such as sewage, toxic chemicals, silt, etc. get mixed with water, the water becomes polluted. 

Long Answer Questions

25. What do CFCs stand for? Name some devices where CFCs are used. Why are CFCs considered pollutants? 

Ans: CFCs stands for Chlorofluorocarbons. These gases are used in air conditioners and refrigerators. CFCs are made up of “Chlorine, Fluorine and Carbon” elements. CFCs are considered pollutants that contribute to the depletion of the ozone layer. 

26. Why is it advised that industries should switch over to cleaner fuels such as CNG and LPG in the Taj Mahal Zone in Agra? 

Ans: This is because the fuel that is not cleaner is causing air pollution in the areas surrounding taj mahal and this results in acid rain which then deteriorates the condition of the taj mahal. 

27. It is said, “CO2 contributes to global warming.” Explain. 

Ans: CO2 is a harmful gas that contributes to air pollution and global warming. CO2 is a gas that is consumed by plants and trees for photosynthesis, so the amount of carbon dioxide is reduced in the atmosphere and in return they give oxygen. But with time industrialisation is happening at speed and trees are being cut at an enormous rate so the level of carbon dioxide is increasing, eventually resulting in the increase in trapping of the heat on earth only, which is increasing earth’s temperature at an alarming rate. 

28. We should plant trees and nurture the ones already present in the neighbourhood. Why? 

Ans: After seeing the issues of global warming in today’s date, there is very much a need to plant more trees and protect the one’s that are already present. As the number of trees is less, so there will be more carbon dioxide in the environment and this causes global warming. Planting more trees will help to decrease the levels of carbon dioxide in the environment and increase the levels of oxygen in the environment. 

29. Explain the traditional way of purifying water to make it fit for drinking.

Ans: Earlier there was not much machinery, so there were not aqua guards or purifiers. But the water was still purified in a more convenient and reliable way, those methods are traditional methods. They are- Filtration: A type of filter or filter rods are used in this method. Candle type filter is a popular household filter. Boiling: Boiling raises the temperature of the water, therefore, killing all the germs and impurities in the water. Chlorination: Chlorine is added to water in the form of tablets or bleaching powder is added to the water. 

30. How can we reduce, reuse and recycle water? 

Ans: Water use can be reduced by:

(a) Closing the tap while brushing.

(b) Changing the leaky tap.

(c) Use a bucket while taking a bath. 

Water can be reused by:

(a) Filtered water from RO can be used for cleaning up the floors. 

(b) Water that is used to wash fruits and vegetables can be used to water plants. 

Water can be recycled by purifying the dirty water by the process of filtration. 

31. Read the paragraph and answer the questions following it. Water is essential for life. Without water, there would be no life. We usually take water for granted for its purity, but we must ensure the quality of water. Pollution of water originates from human activities. Through different paths, pollution reaches groundwater. An easily identified source or place of pollution is called a point source, e.g. municipal and industrial discharge pipes, where pollutants enter the water source. Non–point sources of pollution are those where a source of pollution cannot be easily identified, e.g. agricultural runoff, acid rain etc. 

(i) How do you classify the various sources of water pollution? 

Ans: The various sources of water pollution are- Point source- Can be easily known.  Non-point source- This cannot be easily known. 

(ii) What are the point sources of water pollution? 

Ans: Point source is easily identifiable and a single source of pollution. For example, sewage treatment plants.

(iii) Name any two non-point sources of water pollution? 

Ans: Pollution resulting from multiple sources is known as non-point pollution. For example, Agricultural run-off water and acid rain.

32. Complete the crossword puzzle with the help of clues given below:

Across 

1.  Pollutant which was used in refrigerators and air conditioners. (18)

3. Produced on incomplete combustion of fuels. (14)

6. This chemical protects our crops and is washed into water bodies from the field. (9)

Down 

2. This layer protects us from harmful ultraviolet rays. (5) 

4. It is essential for combustion. (6) 

5. Disease which is caused by drinking contaminated water. (7) 

7. River which is famous in India and sustains most of the northern, central and eastern Indian population. (5)

Ans: 

Topics Covered in NCERT Exemplar Class 8 Science Solutions Chapter 18 Pollution of Air and Water

18.1 Pollution of the Air

18.2 What Causes Air Pollution?

18.3 The Taj Mahal as a Case Study

Greenhouse Effect (18.4)

18.5 Is there anything that can be done?

18.6 What is Water Pollution? 

18.7 How Does Water Become Polluted? 18.8 What is Potable Water, and How Is It Purified?

18.9 Is there anything that can be done?

You'll gain responses to questions like how air and water pollution happens, what are some examples of air and water pollution, and what can be done about it. The chapter raises awareness of pollution and suggests ways to avoid it.