NCERT solutions for class 8 science Chapter 18 Pollution of Air and Water is an extremely essential study tool for CBSE students studying in class 8. NCERT science solutions for Class 8 is arranged by experts of Science to help students in their class 8 exam preparation and to clear the doubts instantly. With the available solutions students can get the answers to the questions provided in the textbook. Our solutions help you in understanding the concepts in a much better way and to prepare for the examinations.
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NCERT Solutions for Class 8 Science Chapter 18: Pollution of Air and Water
1. What are the different ways in which water gets contaminated?
The ways by which water gets contaminated are:
Disposing of garbage in the water.
Industries discharge their harmful chemicals directly into rivers and streams.
Chemical fertilisers, pesticides and weedicides used in agricultural practices get dissolve in water and are washed away into water bodies from the fields.
Discharging untreated sewage into water from household activities.
2. At an individual level, how can you help reduce air pollution?
The following steps can be taken for reduction of air pollution:
i) Avoid the use of personal cars and take public transport.
ii) Dispose of the garbage properly and do not burn it.
iii) Prefer to walk for shorter distances.
iv) Control the emissions from household chimneys and vehicles.
v) Replace the vehicle fuel, diesel and petrol by LPG and CNG.
3. Clear, transparent water is always fit for drinking. Comment.
No, this is not true that clean, transparent water is always fit for drinking. It is possible that such water may carry disease-causing microorganisms. Hence, it is always good to purify water before drinking.
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.
The measures to ensure the supply of clean water to all its residents are as follows:
Chlorine tablets should be made available.
Proper cleaning of the water tank from time to time.
The water supply pipes should not come in contact with the sewage pipes.
5. Explain the differences between pure air and polluted air.
The composition of pure air is about 78% nitrogen, 21% oxygen, and 0.03% carbon dioxide. Other gases such as argon, methane, ozone, and water vapours are also present in small quantities.
When the composition of air is altered by the addition of harmful substances or gases such as nitrogen dioxide, sulphur dioxide, carbon monoxide, and particulate matter, then the air is said to be polluted.
6. Explain circumstances leading to acid rain. How does acid rain affect
Burning of fossil fuels like coal and diesel releases pollutants like sulphur dioxide and nitrogen dioxide in the atmosphere. These pollutants react with the water vapour present in the atmosphere and form sulphuric acid and nitric acid respectively. These acids come down during precipitation and form the acid rain.
Effects of acid rain:
a) It destroys the crops.
b) It corrodes building and structures like the Taj Mahal, Eiffel tower, etc.
7. Which of the following is not a greenhouse gas?
(a) Carbon dioxide
(b) Sulphur dioxide
Option (d) is the correct answer.
8. Describe the ‘Green House Effect’ in your own words.
The greenhouse effect means that the average temperature of the Earth’s surface isincreasing. When the sun’s ray falls on earth, a part of the radiation is absorbed by Earth and a part is reflected back. Greenhouse gases like methane, carbon dioxide and water vapour present in the atmosphere trap these radiations and do not allow heat to escape. This helps in keeping the planet warm and thus helps in survival. But an indiscriminate increase in level of greenhouse gases, can lead to an excessive increase in the Earth’s temperature leading to global warming.
9. Prepare a brief speech on global warming. You have to deliver the
speech in your class.
Global warming is the increase in the average temperature of the Earth’s surface. The main cause of global warming is the increased concentration of greenhouse gases in the atmosphere. The greenhouse gases include methane, CO2, and water vapour. These gases trap the solar radiations released back by the earth, which in turn keeps our planet warm and helps in survival. However, an increase in these gases can lead to an increase in the earth temperature resulting in global warming.
10.Describe the threat to the beauty of the Taj Mahal.
The pollutants in air are discolouring the white marble of Taj Mahal. Acid rains have started corroding the marble. Suspended particulate matter, such as the soot particles emitted by the Mathura oil refinery, has contributed towards the yellowing of the marble. These are some of the threats to the beauty of Taj mahal.
11.Why does the increased level of nutrients in the water affect the survival
of aquatic organisms?
Increased level of nutrients in the water affects the survival of aquatic organisms as these nutrients nourish the algae. Once these algae die, they serve as food for decomposers like bacteria. The decomposition process uses a huge amount of oxygen in water body. This in turn causes a decrease in the oxygen level in the water body, which may kill aquatic organisms.