Pollution of Air and Water Question Answers: NCERT Class 8 Science

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.

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.

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.

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.

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.

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

(d) Nitrogen

Nitrogen is not a green house gas. It is present in air 21%. Carbon dioxide, Sulphur dioxide and methane are the green house gases. 

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.

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.

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.

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.