NCERT Solutions for Class 8th Science

Chapter 18 – POLLUTION OF AIR AND WATER

(Complete Downloadable Chapter Solution PDF file is at the bottom of the page)

 

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

Ans     Water can get contaminated in the following ways:

            1) Waste disposal: Throwing of large quantities of garbage, untreated sewage, dead bodies, and many                    other harmful things, directly into water bodies. In addition to that bathing, washing clothes and                          defecating in water bodies.

            2) Wastes from industries: Iindustries like oil refineries, paper factories etc. discharge harmful                               chemicals into water bodies, causing the pollution of water.

            3) Wastes from agriculture: Pesticides and weedicides used for the protection of crops may get dissolved               in water and are washed into water bodies to pollute them. They also seep into the ground to pollute                     ground water.

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

Ans      The following things can be done to reduce air pollution:

            1) Using public transport or car pool instead of individual car.

            2) Using CNG and LPG as fuel instead of petrol and diesel.

            3) Creating awareness about air pollution among friends and neighbours.

            4) Planting new trees and taking care of the existing ones.

            5) Disposing the garbage in a proper manner and not burning it.

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

Ans     No. This is because water which looks clean may still have disease carrying microorganisms and                           dissolved impurities. So, it is essential to purify water before drinking, for example, 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.

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

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

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

(a) Carbon dioxide

(b) Sulphur dioxide

(c) Methane

(d) Nitrogen

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

Ans     Green House Effect: It may be defined as the natural process of trapping the reflected radiations by the                 earth’s atmosphere and keeping it warm enough to support life. Without this process, life would not have             been possible on the earth. A part of the radiation that falls on the earth is absorbed by it and a part is                   reflected back into space. A part of the reflected radiation is trapped by the atmosphere. The gases                           responsible for this like CO2, methane, nitrous oxide are called green house gases. Due to excessive level               of these gases especially CO2, the average temperature of the earth’s atmosphere is gradually                                   increasing. This is called global warming.

Q.9      Prepare a brief speech on global warming that you have to make in your class.

Ans     Global warming: It may be defined as the heating of the earth or the rise in the temperature of the earth             due to the increase in the level of green house gases in the atmosphere. Green house gases include.........

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

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