Chapter 18 Pollution of Air and Water

By | June 8, 2018
Class 8 | Science | Ch 16 |Pollution of Air and Water| NCERT Solutions

1. What are the different ways in which water gets contaminated ?

Water gets contaminated by :

a) Sewage waste: Waste material from toilet, kitchens, laundry which are discharged in water without proper treatment causes its contamination.

b) Industrial dispose: Harmful and poisonous chemicals are released from industries which contaminate water.

c) Agricultural dispose: Farmers use insecticides , pesticides, fertilisers to increase crop production.These chemical get carried away to the water bodies due to rain and floods which lead to water contamination.

2. At an individual level, how can you help reduce air pollution?

1) By using clean fuels such as LPG and CNG instead of petrol and diesel.

2) We should plant more and more trees to reduce air pollution.

3) We can use public transport and car pooling system to decrease air pollution.

4) Avoid the use of scooter and cars for short distance.

5) We should go by foot or by bicycle instead of using private transport.

6) We should not burn crackers.

7) We should not burn garbage and dry leaves.

8) Controlling the emission from vehicles and household chimney.

3. Clear, transparent water is always fit for drinking. Comment.

Clear and transparent water is not always fit for drinking because it may contain harmful micro-organism , dissolved impurities and salts which are not visible to us.We should purify water before drinking.It can be purified with the help of water purifier or by boiling.

4. You are a member of the municipal body of your town.
Make a list of measures that would help your town to ensure the supply of clean water to all its residents.

To ensure the supply of clean water to all residents the following steps must be taken:

1) The main water source must be build in clean surrounding and should be maintained properly.

2) Water should be treated properly to make it free from harmful germs, chemicals and physical impurities.

3) Leakage in the pipelines should be repaired timely.

4) Chemical methods should be used for purifying water.

5) Awareness programmes should be organised to keep water resources clean.

6) Open defecation in water resources by slum dwellers should be strictly prohibited.

5. Explain the differences between pure air and polluted air.


Pure Air Polluted Air
1 . It contain gases such as Carbon dioxide, Nitrogen, Oxygen, argon , methane, Ozone, water vapours. 2. It includes gases like Sulphur dioxide, Nitogen dioxide, Carbon dioxide, particulate matter.
It is not harmful for human beings.  It is harmful for human beings.

6. Explain circumstances leading to acid rain. How does acid rain affect us?

Acid rain is that rain which contains small amount of acids formed from acidic gases like sulphur dioxide and nitrogen oxides present in polluted air.

The burning of fossil fuels like coal and oil in factories , thermal power plants and oil refineries , petrol and diesel in motor vehicles produce acidic gases like Sulphur dioxide and nitrogen dioxide which go into air and pollute it. Sulphur dioxide and nitrogen dioxide react with water to form sulphuric acid and nitric acid. These acids dissolve in rain water and fall to the earth in the form of acid rain.

Effects of Acid rain

1) It damages the forest trees by destroying their leaves.

2) It kills aquatic animals.

3) It corrodes the statues, building and historical monuments.

7. Which of the following is not a greenhouse gas?
(a) Carbon dioxide
(b) Sulphur dioxide
(c) Methane
(d) Nitrogen

Answer: (d) Nitrogen

8. Describe the ‘Green House Effect’ in your own words.

The warming or heating up of the earth’s atmosphere due to the trapping of Sun’s heat rays by carbon dioxide gas in the atmosphere is called green house effect.Carbon dioxide gas present in the atmosphere allows the heat rays of the Sun to pass through it and reach the earth but prevent the heat rays reflected from the earth’s surface and its objects from passing out of the atmosphere into space.In this way, the Sun’s heat rays remain trapped in the earth’s atmosphere and warm it up.It is due to the warming of earth by green house effect that the earth has become a habitable planet having millions of different life forms on it.

9. Prepare a brief speech on global warming. You have to deliver the speech in your class.

The rise in temperature of Earth atmosphere due to excessive green house effect produced by increase in amount of carbon dioxide gas in the atmosphere is called global warming.Carbon dioxide is added to the atmosphere mainly by the burning of fossil fuels.The carbon dioxide is removed from atmosphere by the plants and trees for making food by photosynthesis.The amount of carbon dioxide in the atmosphere is increasing day by day and the number of plants and trees are decreasing due to deforestation.Global warming is harmful to us because it causes sea levels to rise drastically, can reduce rainfall leading to droughts and it is a serious threat to the existence of life on earth.

10. Describe the threat to the beauty of the Taj Mahal.

Air pollution around Taj Mahal area is discolouring its white marble and also corroding it slowly.The various industries in and around are emitting gaseous pollutants such as Sulphur dioxide and nitrogen dioxide which causes acid rain.The acid present in acid rain react with marble of Taj Mahal monument and corrode it slowly.The suspended particulate matter such as soot particles emitted in the smoke from Mathura oil Refinery is discolouring the pure white marble of Taj Mahal by turning it yellow.

11. Why does the increased level of nutrients in the water affect the survival of aquatic organisms?

The farmers use large amount of chemical fertilisers in the field to increase the yield of crop.The excess fertilisers dissolve in water and run into lakes, rivers and ponds.They cause rapid growth of tiny plants called algae.The algae grow so well that they cover the whole surface of water.When the algae die, bacteria decompose the huge dead mass of algae by using the dissolved oxygen of water in the water bodies.Due to this the amount of dissolved oxygen in the water or lake , river or pond decreases too much and the fish living in this water dies of oxygen starvation.Thus the increased level of nutrients in water affect the survival of aquatic organism.

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