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Pollution Of Air And Water

Class 8th Science CBSE Solution

Exercises
Question 1.

What are the different ways in which water gets contaminated?


Answer:

Water gets contaminated by:

1) Throwing chemical waste into waters.

2) Allowing sewage water into waters.

3) Dumping agricultural wastes into water, which pollutes it.

4) Washing of vehicles, clothes and animals near water bodies.

5) Disposing of Human Remains in the water

6)Disposing of pesticides and herbicides in the water


Question 2.

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


Answer:

An individual can reduce air pollution by following these steps:

1) Car pooling and using public transport whenever possible.


2) By not using vehicles for short distances.


3) By using clean fuels such as LPG and CNG instead of diesel and petrol.


4) Always disposing the garbage properly and not burning it.


5) Controlling the emissions from vehicles and household chimneys.



Question 3.

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


Answer:

Clear and transparent water is not always fit for drinking. Water appears clean, but it may contain some disease causing micro-organisms and other dissolved impurities. Hence, it is advised to purify water before drinking. Purification can be done by water purifying systems or by boiling the water.



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:

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

1) Leakages in pipelines of water should be repaired. Leakage is water wastage.


2) The main water source must be built in clean surroundings and should be maintained properly.


3) Open defection in water resources should be strictly prohibited.


4) Chemical methods such as chlorination must be used for purifying water.



Question 5.

Explain the differences between pure air and polluted air.


Answer:
Question 6.

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


Answer:

When harmful gases like sulphur dioxide (SO2) and nitrogen dioxide (NO2), react with moisture present in air, they form nitric acid (HNO3) and sulphuric acid (H2SO4). These acids when drop down on earth along with rain, is called acid rain.

Effects of acid rain:


1) Acid rains damage crops, decrease fertility of soil and affect aquatic life.


2) Acid rains corrode buildings and structures.



Question 7.

Which of the following is not a greenhouse gas?

(a) Carbon dioxide

(b) Sulphur dioxide

(c) Methane

(d) Nitrogen


Answer:

The correct answer is (d) Nitrogen

Carbon dioxide, Sulphur dioxide, Methane are all greenhouse gases.



Question 8.

Describe the 'Greenhouse Effect' in your own words.


Answer:

The greenhouse effect is the rise in the temperature of the Earth due to increased concentration of greenhouse gases like carbon dioxide, methane, and water vapor in the atmosphere. As these gases trap solar radiations released back by the Earth. This helps in keeping our planet warm and thus, helps in human survival. However, an increase in the amount of greenhouse gases can lead to an increase in the Earth's temperature leading to global warming.


Question 9.

Prepare a brief speech on global warming. You have to deliver the speech in your class.


Answer:

Global warming is one of the greatest challenges that our planet is facing as we have been facing the continuous rise in the average temperature of the Earth’s climate system. It occurs as a result of an increased release of greenhouse gases in the atmosphere. These gases, like carbon dioxide, methane, and water vapor in the atmosphere, trap solar radiations released back by the Earth. This helps in keeping our planet warm. However, an increase in the amount of greenhouse gases can lead to an increase in the Earth's temperature leading to global warming.


Question 10.

Describe the threat to the beauty of the Taj Mahal.


Answer:

Acid rain is a major threat to the beauty of the Taj Mahal. Taj Mahal is made up of marble. When acid rains fall on the monument made of marble, they react with marble to form a powder-like substance that is then washed away by the rain. This phenomenon is known as marble cancer. Also, the soot particles emitted from the Mathura oil refinery located near Agra is leading to the yellowing of the marble of Taj Mahal.


The images show the yellowing effect on the marbles of The Taj Mahal.



Question 11.

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


Answer:

The increased in the level of nutrients in the water leads to an excessive increase in the population of algae in the water bodies. When these algae die, they serve as food for the decomposers. A lot of oxygen is utilized in this process, consequently leading to a decrease in the level of oxygen dissolved in the water body. This in turn causes fishes and other aquatic organisms to die.