Chapter 18

Pollution of air and water

Tick the correct answers

1. Which gas can kill a person when inhaled in excess?
Carbon dioxide
Carbon monoxide
Sulphur dioxide

2. The problem caused by the inhalation of dust particles of air is ________________
Irritation of eyes
Respiratory problem
Brain damage

3. Ultraviolet radiations coming from the sun are stopped by an atmospheric layer rich in______________

4. Ozone hole is found in right above _____________

5. Increasing percentage of carbon dioxide leads to ____________
Global warming 

6. Which of the following is not a cleaner source of energy?
Fossil fuels
Solar energy 
Wind energy

Fill in the blank

1. The increase in the concentration of carbon dioxide causes global warming.
2. Chlorofluorocarbon used in refrigerators, damages the ozone layer of the atmosphere.
3. Water that is suitable for drinking is called potable water.
4. Water is allowed to stand for a date sedimentation tank in the water treatment plant.
5. Taj Mahal is highly affected by acid rain pollution.

Match the following 



Greenhouse gas

Carbon dioxide


Ozone depletion

Industrial effluent

Polluted water

Oxidation of nitrogen

Acid rain

Very short answer question type: 

1. What are the laws of dissolved oxygen from water in water bodies called? of global warming?
Ans: Eutrophication.

2. Name a clean source of energy for producing electricity.
Ans: Hydroelectric energy.

3. What causes acid rain?
Ans:  Sulphuric acid and nitric acid.

4. Name the compound added in the loading tank to purify water.
Ans: Alum.

5. When was the Ganga action plan launched?
Ans: April 1985.

6. Name 2 air pollutants and their sources.
Ans: a) Sulphur dioxide, source- the burning of fossil fuels.
b) Carbon monoxide, sources- incomplete combustion of fossil fuels.

Short answer type 1

1. What is global warming?
Ans: Global warming is the rise in the average temperature of the atmosphere of the earth due to an increase in the greenhouse effect.

2. Give any two methods of control of air pollution?
Ans:  We should use Catholic converter in automobiles that convert harmful gases into harmless gases.
We should grow more plants and trees to reduce carbon dioxide concentration in the air.

3. Define algal bloom?
Ans: Algal bloom
Washing away of fertilizer into water bodies causes increase growth of algae and other weeds in the water bodies. This is called algal bloom.
The process of nutrient enrichment of water bodies that stimulates the growth of aquatic plants like algae that may result in depletion of dissolved oxygen is called eutrophication.

4. What are the natural sources of air pollution?
Ans: Air pollutants may come from natural sources like smoke and dust that arise from forest fire or volcanic eruption.

5. List two ways of reducing water pollution?
Ans: Dead bodies should be cremated or buried and not disposed of in a River or a Lake.
Educating the public about the harmful effects of water pollution.

6. What is biological magnification?
Ans: By increasing the concentration of harmful chemical substances like pesticides in bodies of organisms at the Trophic level of the food chain is called biological magnification.

Short answer type 2 questions 

1. What are the damaging effects of ozone layer depletion?
Ans:  Harmful ultraviolet radiation reaching the earth causes various diseases in human beings such as cataract, skin cancer, damage of eyesight, etc.
Harmful UV radiation can bring about changes in the gene structure leading to mutations.
Harmful UV radiations cause damage is too early and the element status of Fishers, crabs, and other animals. 

2. What are the main causes of water pollution?
Ans: Domestic sewage liquid waste from a kitchen and the toilet, discharge into river through sewer systems causing water pollution.
Human activities batting of human beings and animals in or near lakes reverse etc., pollutes the water bodies.
Oil splits from huge tankers are one of the major causes of water pollution that affects marine plants and animals.

3. Discuss the damaging effects of acid rain?
Ans:  Acid rain makes the water of lakes and rivers acid leading to the destruction of aquatic plants and animals.
Acid rain destroys monuments and buildings.
Acid rains promote corrosion of metallic objects like railways bridge and gates.

4. Mr. Mehta has a CNG – fueled car. But due to this, he has to stand in long queues. He’s also in favor of regular pollution check in vehicles and uses catalytic converter in his car while Mr. Singh uses petrol in his car and also advises Mr.Mehta to shift to petrol instead of the CNG  to get rid of the queue problem.

a) Do you think Mr. Mehta should shift to petrol instead of CNG? Why/ why not?
Ans: No, Mr. Mehta should not shift to petrol instead of CNG as CNG is a cleaner fuel and is good for the environment.

b) Is it right to use a catalytic converter in the car? Why/ why not.
Ans:  It is right to use a catalytic converter in the car because they convert the harmful gases into harmless gases.

5. Write the steps involved in the treatment of water in the water treatment plant.
Ans: Sedimentation, loading, filtration chlorination, and storage.

Long answer questions

1. Discuss the harmful effects of air pollution?
Ans: Air pollution can cause various health problems.
-> Carbon monoxide is a very poisonous gas.  When inhaled in excess it combines with hemoglobin of blood and forms of Carboxyhemoglobin.  This prevents it from carrying oxygen that causes unconsciousness or even death.
-> Oxides of Sulphur dioxide and Sulphur trioxide cause various respiratory problems and may even damage the lungs.
-> Oxides of nitrogen cause lung conjunction.
-> Fumes coming out of chemical industries cause irritation in eyes, nose and throat.
-> Particles of lead oxide present in automobile exhaust can cause mental disorder and brain damage.
-> Particles of dust in air can cause bronchitis.
-> Smog that is formed from smoke and fog causes breathing difficulties like asthma, cough and wheezing. They also reduce visibility.

2. (a) What is the greenhouse effect? Name two greenhouse gases.
(b)Discuss global warming and its harmful effects.
Ans: (a)The phenomenon whereby the earth’s atmosphere traps solar radiation because of the presence of gases like carbon dioxide nitrogen oxide, water vapors methane, and CFCs is called the greenhouse effect.
The two greenhouse gases are carbon dioxide and methane.
(b)Global warming is the rise in the average temperature of the atmosphere of the earth due to an increase in the greenhouse effect
Damaging effects of global warming
-> Polar ice caps would melt and water would flow into the sea.
-> If the level of water in the sea increases, low lying areas near coastal would be submerged.
-> Climate and rainfall patterns would be changed.
-> It would also affect agriculture and thus the production of food.

3. Briefly discuss the steps involved in the purification of River or Lake water.
  • Water from River or lake is first pumped into a sedimentation tank. Here, the large insoluble impurities settled down at the bottom. Some light insoluble impurities remain suspended.
  • The water is passed to a loading tank where these suspended impurities also settle down faster by adding some chemicals like alum.
  • Then, water is passed to the filtration Here, it passes through the layers of sand, gravel, and charcoal which filter the remaining impurities.
  • Then, chlorine is added to the water which kills all the germs present in the water.
  • The water is now fit for safe drinking.

1. What would have happened if there is no greenhouse effect?
Ans: If there was no greenhouse effect, the earth’s surface would be too cold to sustain life.

2. How does excessive use of fertilizer cause eutrophication?
Ans: Eutrophication: A major problem with the use of fertilizers occurs when they are washed off the land by rainwater into the rivers and lakes. the resulting increase of nitrates or phosphate in the water encourages algae growth, which forms a bloom over the water surface.

3. Which one of the following is safe for drinking water: River or well water? Give reason.
Ans: Using water from wells for drinking purposes is safe in comparison to River water. This is because river water contains heavy metals.