NCERT Solutions for Class 8 Science - Pollution of Air and Water

NCERT TEXTBOOK QUESTIONS SOLVED
 

Q. 1. What are the different ways in which water gets contaminated?
Ans. Water gets contaminated in the following ways:
(i) Many industries discharge harmful chemicals to rivers and streams.
(ii) Water gets contaminated when sewage is disposed off in rivers.
(iii) Pesticides, weedicides and other chemicals also dissolve in water and get contaminated.
(iv) Breeding of microorganisms makes water polluted.
 

Q. 2. At an individual level, how can you help reduce air pollution?
Ans. By this process we can reduce air pollution:
(i) We should plant trees to reduce the level of carbon dioxide and air pollution.
(ii) By using CNG and unleaded petrol in our vehicle.
(iii) By using public transport as far as possible.
(iv) By giving general awareness about air pollution to our family and friends.

 Q . 3. Clear, transparent water is always fit for drinking. Comment.
Ans. Clear, transparent water is always fit for drinking. This is not true, because many microorganisms are present in it. So we should clean it by boiling.
 

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.
Ans. A list of measures that would help our town to ensure the supply of clean water to all its residents–
(i) Proper cleaning of water tank.
(ii) Chlorine tablets should be made available.
(iii) To get clean water in every household, it is necessary that water reaching the houses should be treated.
 

Q. 5. Explain the differences between pure air and polluted air.
Ans. Pure air is free from germs and harmful gases. It contains 78% nitrogen, 21% oxygen and small amount of other gases and dust particles.
Polluted air contains harmful gases and unwanted substances.
 

Q. 6. Explain circumstances leading to acid rain. How does acid rain affect us?
Ans. Some pollutants like sulphur dioxide and nitrogen dioxide react with the water vapour present in the atmosphere to form sulphuric acid and nitric acid. The acid drops down with rain, making the rain acidic. This is called acid rain. Acid rain affects us in many ways.
(i) Acid rain corrodes the marble of the monument.
(ii) Acid rain damages building and sculptural materials.
(iii) Acid rain damages fresh water also.
(iv) Acid rain also damages our crops and makes it poisonous.
(v) Acid rain damages the leaves of plants.
 

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

Q. 8. Describe the ‘Greenhouse Effect’ in your own words:
Ans. Greenhouse effect means warming of environment. When the sun rays reach on earth, a part of the radiation that falls on earth is absorbed by it and a part is reflected back into space. A part of the reflected radiation is trapped by the atmosphere. This trapped radiation further warms the earth. This is called Greenhouse effect. CO₂ is one of the gases responsible for this effect.
 

Q. 9. Prepare a brief speech on global warming. You have to deliver the speech in your class.
Ans. Continuous increase in temperature of the earth is called global warming. There are many reasons for it. One of them is increase in population. Increase in the number of vehicles is also one of the causes. Pollution of air has also increased the global warming. Cutting trees, grazing the plants by animals increase the global warming. 

Q . 10. Describe the threat to the beauty of the Taj Mahal.
Ans. Over the past two decades, India’s most famous tourist attraction Taj Mahal located at Agra, has become a matter of concern. Experts have warned that air pollution is discolouring its white marble. So it is not only living organisms but also the non-living things like buildings, monuments and statues get affected by polluted air. 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 particles emitted by the Mathura Oil Refinery, have contributed to the yellowing of the marble.
The Supreme Court has taken steps to save the Taj. It has ordered the industries to switch to cleaner fuels like CNG ( Compressed Natural Gas) and LPG (Liquefied Petroleum Gas). Moreover, the automobiles should switch over to unleaded petrol in the Taj zone.
 

Q . 11. Why does the increased level of nutrients  in the water affect survival of aquatic organisms?
Ans. Excessive quantities of chemicals get washed away from the fields. These act as nutrients for algae to flourish. Once these algae die, they serve as food for decomposers like bacteria. A lot of oxygen in water body gets used up. This results in the decrease in the oxygen level which may kill aquatic organisms.