NCERT Solutions for Class 8 Science Chapter 18 Pollution of air and water Questions and Answers

Pollution of air and water Questions and Answers Class 8


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

Solution:- Different ways in which water gets contaminated are as follows:-

  1. By disposal of domestic sewage into the water bodies. 
  2. Discharge of industrial sewage directly into water bodies, like – lakes, sea etc.
  3. Bathing of human beings and animals in or near the river lakes etc, also makes water contaminated.
  4. Washing clothes near the water bodies, like lakes and rivers.
  5. Chemicals used for agriculture like fertilizers, pesticides and weedicides dissolve in water and are washed away into water bodies which makes water polluted.

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

Solution:-  At an individual level, I can do the following things to reduce air pollution:-

  1. I will use public transport as far as possible. To avoid the pollution that comes from cars.
  2.  I will plant more and more trees in my surrounding. To inhale non-polluted air.
  3.  I will not use vehicles for short distances.
  4. I will help people to reduce air pollution and plant more trees. This will help our environment get clean.
  5. I will use CNG and unleaded petrol in my vehicle.

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

Solution:-  No, it is not true that clean and transparent water is always fit for drinking. It is possible that they may infect our body or may carry harmful diseases that can harm our body. Thus, it is good to purify water before drinking. It is good for our health. You can purify it by any method, like -boiling etc.

Q.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.

Solution:-  A list of majors that would help our town to ensure the supply of clean water to all its residents are as follows:-

  1. Chlorine tablets or bleaching powder should be added in the water so that water can be purified. 
  2. There should be proper cleaning of the water tank before filling it with clear water.
  3. The water supply pipes should not come in contact with the sewage pipe and should be always clean and should avoid leakage.

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

Solution:- Pure air contains 21% oxygen, 78% nitrogen, 0.03% carbon dioxide and some other gases such as methane, neon etc.

It is free from harmful gases and dust when it is contaminated by unwanted substances such as sulphur oxide, and nitrogen dioxide and the air is said to be polluted.

Pure air, contains no harmful gases and is good for living organisms, and polluted air contains harmful gases that are not good for both living and nonliving organisms.

Polluted air can harm our body and will make it hard to breathe in the environment.

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

Solution:- It is a chemical reaction, when some pollutants like sulphur dioxide and nitrogen dioxide get mixed with the atmosphere, they react with the water vapour present in the atmosphere to form sulphuric acid and nitric acid.

These acids fall down with the rain, making the rain acidic. It is called acid rain. It is very harmful to live organisms.

Acid rain Affects us in many ways:-

  1. It damages the marble of the monuments and buildings. 
  2. It increases the acidity of soil which leads to the loss of soil fertility.
  3.  It makes the water acidic leading to the destruction of aquatic plants and animals.
  4. It damages crops.
  5.  It causes skin irritation. 

Q.7 Which of the following is not a greenhouse gas?

  1. Carbon dioxide
  2. Sulphur dioxide 
  3. Methane
  4. Nitrogen

Answer is (d) Nitrogen

Q.8 Describe the ‘GreenHouse Effect’ in your own words.

Solution:-  The warming up of Earth’s atmosphere due to the trapping of the sun’s heat range by carbon dioxide gas in the atmosphere is called the greenhouse effect.

It also causes global warming, the undue rise in the temperature of the earth’s atmosphere due to the excessive greenhouse effects produced by increasing the amount of carbon dioxide gas in the atmosphere is called global warming.

Without this process, life would not have been possible on earth but now it’s been a threat to life. When the sun’s rays fall on earth, a part of the radiation is absorbed by the earth and a part is reflected back into space.

Greenhouse gases present in the air trap this radiation and do not allow heat to leave. This helps in keeping our planet in  Survival but excessive amounts of CO2 in the air also harm our planet.

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

Solution:- A very refreshing, Good morning to one and all present here.

Respected teacher and all my dear friends, today I am going to give a speech on the topic of global warming. 

The rise in the temperature of the Earth’s atmosphere is known as global warming. There are many reasons for this but the main reason is the greenhouse effect.

It releases the gases like carbon dioxide, methane, and chlorofluorocarbon into the atmosphere. These gases trap the heat of the sun and do not allow them to leave.

This leads to an excessive rise in the temperature of the earth. This hurts many people, animals and plants. 

Some damaging effects of global warming are as follows:-

  1. Ice would melt and water would flow into the sea. This will cause the sea to rise and small Islands will be covered by the water. This will lead to a flood.
  2. Climate and rainfall patterns change.
  3. It would also affect agriculture and destroy many forests.
  4.  Sea rise will harm people living in coastal areas.
  5. Increase the intensity of the storm.

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

Solution:-  Taj Mahal is losing its white shiny look and getting discoloured.  The main reason for its discolouration is due to acid rain and air pollution. Mathura oil refinery has contributed to the yellowing of the marble.

This means not only living organisms but non-living organisms are also being affected by air pollution and acid rain.

Some steps have been taken by the supreme court to protect the Taj Mahal:-

  1.  Industries are ordered to switch to cleaner fuels like CNG and LPG. 
  2. The automobiles should steile out to unleaded petrol in the Taj zone.

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

Solution:- Increased level of nutrients in the water body, will lead to the excessive growth of algae. When these algae die they serve as food for decomposers.

In this process, a lot of oxygen is used, which results in a decrease in the oxygen level in the water body. This will make aquatic organisms hard to breathe in the water because of the less Oxygen and they may die.

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