NCERT Solutions for Class 8 Science Chapter 18 Pollution of Air and Water

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Pollution of Air and Water NCERT Solutions for Class 8 Science Chapter 18

Class 8 Science Chapter 18 Pollution of Air and Water Exercise Questions and Answers

Question 1.
What are the different ways in which water gets contaminated?
Answer:
Water gets contaminated in the following ways:

1. Many industries discharge harmful chemicals into rivers and streams.
2. Chemical fertilizers, pesticides, and weedicides used in agriculture dissolve in water and are washed away into water bodies from the fields.
3. Throwing of untreated sewage directly into rivers.
4. Many industries release hot water into rivers.

Question 2.
At an individual level, how can you help reduce air pollution?
Answer:
At an individual level we can help in reducing air pollution by the following methods:

1. We can plant trees and nurture the ones already present in the neighborhood.
2. We can also educate the people against burning the dried leaves and plants and advise them to put them in a compost pit.
3. We should encourage the use of bicycles or the practice of carpooling instead of using individual cars.
4. The use of clean fuels such as LPG or CNG should be encouraged.

Question 3.
Clear, transparent water is always fit for drinking. Comment.
Answer:
No, clear and transparent water even without smell, may contain bacteria, viruses, etc., which are not visible to the eyes. Drinking such water can cause illness of various kinds. Therefore, we must drink purified and potable water after boiling.

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:
The following steps could be taken:

1. First of all, procurement of the required amount of water for all residents should be ensured.
2. Then it should be ensured that water treatment plants get the optimum amount of water every day.
3. Wastage of water by leakage at various places should be taken into account. The leakage should be repaired immediately on war-footing.
4. The municipal body must keep a sufficient number of water tankers ready to meet any emergency (challenging situations).
5. Water is also stolen by a number of unscrupulous parties. These are to be taken to task and punished and measures should be taken so that this should not occur again.

Question 5.
Explain the differences between pure air and polluted air.
Answer:
Air is a mixture of gases.

Pure air contains about 78% (by volume) nitrogen, 21% oxygen and a small but a definite amount of carbon dioxide, argon, methane, neon, water vapour etc.

When the air is contaminated by unwanted substances which have a harmful effect on both the living and non-living components it is called polluted air.

Question 6.
Explain circumstances leading to acid rain. How does acid rain affect us?
Answer:
Gases like sulfur dioxide and nitrogen dioxide react with water vapor present in the atmosphere to form sulphuric acid and nitric acid. These acids come down with rainwater, making the rain acidic. This is known as acid rain. , Acid rain corrodes the marbles of the monuments.

This phenomenon is known as “Marble cancer”. If acid rain occurs in the agricultural field, it spoils or kills the plants/ crops in the field. The acid rains also spoil the quality of agricultural soil of the field because the soil becomes acidic. The acidic soil is unfit for crop production.

Question 7.
Which of the following is not a greenhouse gas?
(a) Carbon dioxide
(b) Sulphur dioxide
(c) Methane
(d) Nitrogen
Answer:
(b) Sulphur dioxide is not a greenhouse gas.

Question 8.
Describe the ‘Greenhouse effect’ in your own words.
Answer:
In a greenhouse (in a nursery or elsewhere) Sun’s heat Sun is allowed to get in but is not allowed to get out. The trapped heat warms the greenhouse. The trapping of the radiations by the Earth’s atmosphere performs a similar function. The trapped radiations further warm the Earth. This effect of the atmosphere is called the greenhouse effect. Without this process, life would not have been possible on Earth because of the low temperatures. C02 is one of the gases responsible for this effect. Other gases like methane, nitrous oxide, water vapour also contribute to this effect. They are also called greenhouse gases.

Question 9.
Prepare a brief speech on global warming. You have to deliver the speech in your class.
Answer:
The undue rise in the temperature of Earth’s atmosphere due to the excessive greenhouse effect produced by increasing amounts of carbon dioxide gas in the atmosphere is called global warming.

It has become a major concern for all countries because a slight increase in atmospheric temperature can cause serious consequences to all living beings. Many countries have reached an agreement to reduce the emissions of greenhouse gases so as to reduce global warming. The Kyoto Protocol is such an agreement.

An important step to reduce the effects of global warming is to minimize the burning of fossil fuels because it emits greenhouse gases such as carbon dioxide, methane, nitrous oxide, chlorofluorocarbons. Stress should be laid on the use of alternative sources of energy like solar and wind energy.

Class 8 Science Chapter 18 Pollution of Air and Water InText Questions and Answers

18.1 Air Pollution

Activity 18.1

On the basis of your experiences, compare the quality of air at the places given below :

1. A park and a busy road.
2. A residential area and an industrial area.
3. A busy traffic intersection at different times of the day e.g., early morning, afternoon, and evening.
4. A village and a town.

Answer:

1. A park is full of fresh air, whereas air around a busy road is very polluted because of fumes, smoke, dust, and sound.
2. A residential area is also polluted but as compared to an industrial area, it is almost negligibly polluted. The industrial area is extremely polluted with chemical pollutants, toxic gases, etc.
3. In the early morning, the traffic intersection is almost free from any pollutants, but in the afternoon it becomes very polluted due to smokes left out by vehicles, etc. In the evening, the place is extremely polluted.
4. A village is usually not so polluted as a town. A town has polluted air, polluted water and a lot of other pollution like sound pollution, etc.

Question 1.
Do you know, where the smoke could have come from?
Answer:
Industries and automobiles contribute to smoke in the atmosphere.

18.2 How does Air Get Polluted?

Question 2.
Have you noticed how rapidly the number of vehicles is increasing in our cities?
Answer:
Yes, the number of vehicles is increasing rapidly in our cities.

Question 3.
Have you heard of the ozone hole?
Answer:
Yes, I have heard about it. It is mainly due to the emission of chlorofluorocarbons.

Activity 18,3

Question 1.
Prepare a table using the pollutants mentioned above. You may even add more data to the following Table.
Answer:

Air Pollutants	Sources	Effects
Carbon dioxide	Vehicles, Industries	Respiratory diseases, Global warming
Carbon monoxide	Vehicles, Industries	Respiratory diseases can even kill a person
Chlorofluorocarbons (CFCs)	Refrigerators, air conditioners, aerosol sprays, etc.	Depletion of the ozone layer

18.3 Case Study: The Taj Mahal

Question 4.
Discuss with your elders and see what they have to say about the condition Of the Taj, 20 or 30 years ago! Try to procure a picture of the Taj Mahal for your scrapbook.
Answer:
The Taj- Mahal used to look extra-ordinarily white and beautiful during full moon night. But today it is pale and does not look so charmful.

Question 5.
I am reminded of the chapter on crops. I wonder whether acid rain affects the soil and plants also.
Answer:
Yes, it makes the soil of the field acidic, which is not suitable for crops. If there are crops and plants in the field, the acid rain kills these plants and crops.

18.4 Greenhouse Effect

Question 6.
Boojho is surprised to hear that an increase in the earth’s temperature by even as little as 0.5°C can have such a serious effect!
Answer:
Yes, this little increase in temperature can create global warming and due to global warming sea levels will rise and many coastal areas will be flooded causing a huge loss of life and property. Rainfall patterns will also change affecting crop production. The glaciers of Gangotri in the Himalayas had started melting because of the slight rise in temperature. This, in fact, can bring disaster.

18.5 What can be done?

Question 7.
What can we do to reduce air pollution?
Answer:

1. The use of CNG and unleaded petrol in vehicles will decrease air pollution.
2. Saying no to crackers may also reduce air pollution to some extent.
3. Fuels like solar energy, hydropower, and wind energy should be given priority over fossil fuels for our energy requirements.
4. Walking or going by bicycle should be encouraged.
5. Instead of using their own cars, people should encourage the habit of carpooling.
6. Van Mahotsava should be celebrated by planting lakhs of plants and trees.
7. These practices may be helpful in reducing air pollution.

Question 8.
Do you know about the “Say no to Crackers” campaign which was organized by children from many schools?
Answer:
The campaign “Say no to crackers” organized by school children brought about a big difference to the air pollution level around Diwali.

Activity 18.4

Question 1.
Discuss in your class the impact of each of these options on the quality of air.
Answer:
Going on foot or by bicycle will not cause any pollution at all. Traveling by bus, other public transport system or by carpool will cause pollution up to an extent while using a car individually will cause much pollution.

Question 9.
Do you know about Van Mahotsav, when lakhs of trees are planted in July every year?
Answer:
Yes, I know about it. This is done to save the environment and make our earth green.

Question 10.
Paheli thought it would be a better option to put them (dried leaves) in a compost pit rather than burning them. What do you think?
Answer:
Paheli is justified in suggesting so. The burning .of dried leaves and dried plants are dangerous because it emits out gases like C0₂ and CO in the atmosphere, which cause air pollution. If these are put in a compost pit, they will produce very useful manure for the plants.

18.6 Water Pollution

Activity 18.5

Question 1.
Try to collect samples of water from a tap, pond, river, well, and lake. Pour each into separate glass containers. Compare these for smell, acidity, and color. Complete the following table:
Answer:

	Smell	Acidity	Colour
Tap water	Smells	Yes	Dull
Pond water	Smells a lot	Yes	Dirty and muddy
River water	Smells a little	No	Little colorless
Well water	Smells	Yes	Dull
Lake water	No smell	No	No color

18.7 How does Water get Polluted?

Question 11.
What are the factors responsible for the pollution Of rivers?
Answer:
The sewage water from homes and toxic chemicals mixed with water from factories flow into the rivers and these get polluted. Besides, people also throw solid pollutants in the water body from time to time.

Question 12.
What steps can be taken to restore the river Ganga to its past glory?
Answer:

1. Laws should be made and strictly implemented so that pollutants are not disposed of directly into Ganga.
2. Water treatment plants should be installed in all industrial areas.

Question 13.
How would the disposal of garbage, etc. affect the living organisms in the river?
Answer:
Disposal of garbage into the river pollutes river water by increasing the toxicity of water or by depleting the oxygen content of water. This may lead to the death of living organisms in the river.

Recall Activity 18.6

Question 1.
Do you remember how the sewage was collected from your home and where it went thereafter?
Answer:
In a home or a public building generally, one set of pipes brings clean water and another set of pipes takes away wastewater. The pipe carrying wastewater is called sewer. These sewers from sewerage which is like a transport system that carries sewage from the point of being produced to the point of disposal i.e., treatment plant.

At the treatment plant, the wastes are treated and the physical, chemical, and biological matters that contaminate it, are removed.

Question 2.
Can groundwater get polluted by sewage? How?
Answer:
Sewage water seeps down to ground¬water and mixes up with groundwater. Thus, making it polluted. Groundwater polluted by sewage may contain bacteria, viruses, fungi, and parasites which can cause diseases like cholera, typhoid, and jaundice.

18.8 What is Potable Water and How is Water Purified?

Activity 18.7

Question 1.
Why do we need to filter water before drinking?
Answer:
The unfiltered water contains dust particles and chemical substances, which is harmful to the health of people who drink it. If filtered, these substances are removed. water and water become fit for drinking.

Question 2.
Where do you get your drinking water from?
Answer:
I get drinking water supplied by Delhi Jal Board.

Question 3.
What will happen if we drink polluted water?
Answer:
If we drink polluted water, we may suffer from water-borne diseases such as jaundice, dysentery, hepatitis, cholera, etc.

18.9 What can be done?

Activity 18.8

Question 1.
What are the common water-borne diseases in the community?
Answer:
Diarrhea, dysentery, cholera, jaundice, etc. are some of the common water-borne diseases in the community.

Question 2.
Which are the governmental and non-governmental organizations working in this field? What are the measures being taken by them for generating awareness?
Answer:
Many governmental organizations like the public welfare department, hospitals, etc. are working in this field. Besides, NGOs like Deepalaya, Prayas, Nyas, etc. are also working in this area. These organizations are generating awareness through field works, billboards, advertisements, etc.

Question 14.
Think of your daily routine how can you save water?
Answer:
We can use only the required amount of water for our daily work like bathing, washing clothes, shaving, etc. Besides, water used for washing fruits and vegetables can be used for cleaning floors, vehicles, or watering the plants.