NCERT Solutions for Class 8 Science Chapter 18 Pollution of Air and Water are part of NCERT Solutions for Class 8 Science. Here we have given NCERT Solutions for Class 8 Science Chapter 18 Pollution of Air and Water.

Board CBSE
Textbook NCERT
Class Class 8
Subject Science
Chapter Chapter 18
Chapter Name Pollution of Air and Water
Number of Questions Solved 11
Category NCERT Solutions

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

NCERT TEXTBOOK EXERCISES

Question 1.
What are the different ways in which water gets contaminated?
Answer.
Water gets contaminated due to the addition of substances harmful to health. Sewage, agricultural chemicals, and industrial waste are some of the major contaminants of water.

Question 2.
At an individual level, how can you help to reduce air pollution?
Answer.
At the individual level we can do the following things to reduce air pollution:

  1. Use CNG and unleaded petrol instead of ordinary petrol and diesel.
  2. Use public transport as far as possible.
  3. Generate awareness about air pollution among the members of our family and friends.
  4. We can plant trees and nurture the ones already present in the neighborhood.

Question 3.
Clear, transparent water is always fit for drinking. Comment.
Answer.
No, water which looks clean may still have disease-carrying microorganisms and dissolved impurities. Hence, it is not always fit for drinking, so it is essential to purify water before drinking, say for example by boiling process.

Question 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.
Answer.
Following are some of the measures that would help our town to ensure the supply of clear water to all its residents:

  1. Make the supply system leakproof as a lot of drinking water is being wasted through the leakages.
  2. Proper cleaning of the water tank from time to time.
  3. Chlorine tablets should be made available.
  4. The water supply pipes should not come in contact with the sewage pipes.

Question 5.
Explain the differences between pure air and polluted air.
Answer.
Pure air is free from any pollutant, has no smell, is soothing, and not irritating to the eyes. Whereas polluted air gives a filthy smell and people cannot breathe in ut. If people inhale such (impure or polluted) air, they may suffer from various breathing, heart, and lung problems. Even sometimes people die inhaling polluted air.

Question 6.
Explain circumstances leading to acid rain. How does acid rain affect us?
Answer.
Pollutants like sulphur dioxide and nitrogen dioxide react with the water vapour present in the atmosphere to form sulphuric acid and nitric acid. These come down with the rain, making the rain acidic. This is called acid rain.
Acid rain affects us in many ways, e.g.

  1. Acid rain removes basic nutrients such as calcium from the soil.
  2. Acid rain increases the corrosion of metals.
  3. Acid rain damages buildings and sculptural materials.
  4. The low pH of add rainwater changes the rate of metabolism of some organisms.
  5. Add rain causes damage to freshwater life, e.g., decrease in fish population of lakes.
  6. Add mists cause direct damage to the leaves of plants.

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

Question 8.
Describe the ‘Green House Effect’ in your own words.
Answer.
The sun’s rays when fall on the earth’s surface, warm it. Some of the sun’s rays are absorbed by the earth’s surface and left out rays are reflected back into space. Some of these rays are trapped by gases like C02, methane, etc. in the atmosphere, and these are not allowed to go out of the earth’s atmosphere.

These trapped rays begin to warm the earth’s surface. This causes heating of the earth’s atmosphere. This effect is named the Greenhouse effect because this is exactly like the greenhouse effect in a nursery.

Question 9.
Prepare a brief speech on global warming. You have to deliver the speech in your class.
Answer.
Today, global warming has appeared as one of the most severe threats to humankind. On one hand, carbon dioxide is added to the atmosphere due to human activities, by the other, as forest areas are also decreasing.

Question 10.
Describe the threat to the beauty of the Taj Mahal.
Answer.
Over the past 2 decades, India’s most famous tourist attraction, the Taj Mahal located at Agra, has become a matter of great concern. Experts have warned that air pollution is discolouring its white marble. So it is not only living organisms that get affected by polluted air but also the non-living things like buildings, monuments, and statues that are going to be affected.

The industries located in and around Agra like rubber processing, automobiles, chemicals and especially, the Mathura Oil Refinery have been responsible for producing pollutants like sulphur dioxide and nitrogen dioxide. These gases react with the water vapour present in the atmosphere to form sulphuric acid and nitric acid. These come down with the rain, making the rain acidic. This is called acid rain. Acid rain has resulted in corrosion of the marble of the monument. The phenomenon is also called “Marble cancer”. Suspended particulate matter, such as the soot particle emitted by the Mathura oil refinery, has contributed to the yellowing of the marble.

The Supreme Court has taken several steps to save the Taj Mahal. It has issued orders for the industries to either switch to cleaner fuels like CNG (Compressed Natural Gas) and LPG (Liquefied Petroleum Gas) or to move to faraway places. Moreover, the automobiles should switch over to unleaded petrol in the Taj Mahal Zone.

Question 11.
Why does the increased level of nutrients in the water affect the survival of aquatic organisms?
Answer.
Chemicals used as fertilizers in agriculture dissolve in water and are washed away into water bodies from the field. The excessive quantities of chemicals like nitrates and phosphates which are present in fertilisers act as nutrients for algae to flourish. Once these algae die, they serve as food for decomposers like bacteria. They use up a lot of oxygen. This results in a decrease in the oxygen level which is harmful to the survival of other organisms.

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