pollution-of-air-and-waterWHERE cd.courseId=12 AND cd.subId=16 AND chapterSlug='pollution-of-air-and-water' and status=1SELECT ex_no,page_number,question,question_no,id,chapter,solution FROM question_mgmt as q WHERE courseId='12' AND subId='16' AND chapterId='381' AND ex_no!=0 AND status=1 ORDER BY ex_no,CAST(question_no AS UNSIGNED) CBSE Class 8 Free NCERT Book Solution for Science

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Chapter 18 : Pollution of Air and Water


  • When some harmful substance or some polluted gases are mixed in air, then the air becomes impure. It contaminated the air, this is called as air pollution.
  • The substances which contaminate air and water called as pollutants.
  • The major pollutants of air are the carbon dioxide, carbon monoxide, nitrogen oxides, methane and Sulphur dioxide.
  • When the concentration of carbon dioxide increases in the atmosphere which may leads to the increase in the temperature of the Earth. It may lead to global warming.
  • When some harmful substances or some impurities dissolved in water. This is called as water pollution.
  • Water is contaminated by sewage, agricultural and industrial waste.
  • Potable water is fit for drinking because it is purified.
  • Water is the natural resource which is precious. So, we have to conserve it.
  • Chemical contamination is done by chemical fertilizers and detergents contains water.

Exercise 1 ( Page No. : 253 )
Q:
A:

Water gets contaminated in following ways:

  • By untreated sewage
  • When sewage water is disposed into rivers.
  • By industrial waste.
  • Excessive amount of pesticides and fertilizers are used by farmers. These chemical seeps through the soil and make water contaminated.

Exercise 1 ( Page No. : 253 )
Q:
A:

At an individual level, air pollution can be reduced in following ways:

  • By using public transport as much as possible.
  • Avoid the use of vehicles for short distances.
  • Avoid the use of petrol and diesel.
  • Use clean fuel like LPG and CNG.
  • Dispose the waste properly.
  • Control the emission of ashes from household chimneys.

Exercise 1 ( Page No. : 253 )
Q:
A:

No, clear and transparent water is always fit for drinking because it contains some disease causing bacteria and some microorganisms, some other dissolved contaminants etc. It might appear clean but it is still unfit for drinking. We can purify water by boiling it or by purifying it by the machines.


Exercise 1 ( Page No. : 253 )
Q:
A:

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

  • The area must be clean around the water pipes.
  • Chlorination must be used for purifying water.
  • The main source of the water should be maintained properly.

Exercise 1 ( Page No. : 253 )
Q:
A:

Pure air contains 78% nitrogen, 21% oxygen, 0.03% carbon dioxide and other gases that present in the minute quantity. When some harmful substances or other poisonous gases mixed up in the air then the air become polluted. When these pollutants react with water and lead to acid rain.


Exercise 1 ( Page No. : 253 )
Q:
A:

Burning of fossil fuel releases a variety of pollutants such as nitrogen oxide and Sulphur oxide in the atmosphere. These reacts with the water vapours which are present in the atmosphere to form nitric acid and sulphuric acid. These acids comes down with the rain and this may leads to acid rain. Acid rain affects us in the following ways:

  1. It damages crops
  2. It corrode buildings
  3. It cause health problems

Exercise 1 ( Page No. : 253 )

Exercise 1 ( Page No. : 253 )
Q:
A:

Green house effect is caused by green house gases. When the average temperature of the earth increases due to the increment in the level of the carbon dioxide in the atmosphere. When solar radiations reaches the earth, some of these radiations are absorbed by Earth and released back into the atmosphere. But the green house gases trap the solar radiation and do not allow the heat to leave. The excessive increase in the temperature of Earth leads to global warming.


Exercise 1 ( Page No. : 253 )
Q:
A:

When the concentration of green house gases like carbon dioxide, methane and Sulphur dioxide increases in the atmosphere. It leads to the increase in the temperature of the Earth’s surface. These gases traps the solar radiations and released back to the Earth. It keeps our planet warm. The excessive increase in the Earth’s temperature leads to global warming.


Exercise 1 ( Page No. : 253 )
Q:
A:

The major threat to the beauty of Taj Mahal is acid rain. Taj Mahal is made up of marbles. When acid rain falls on it, then it reacts with the marble and form a powder like substances which is washed away by the rain. This is also called as marble cancer. The yellowing of marble is because of the acid rain.


Exercise 1 ( Page No. : 253 )
Q:
A:

The increased level of the nutrients in the water affect the survival of aquatic organism which may leads to the increases population of algae. The level of oxygen is decreases in the water because a lot of oxygen is utilized in this process. When the dissolved oxygen is decreased, then the organisms died who lived in the water.