Pollution of Air and Water – Case-based Questions with Answers

Rohan’s doctor advised him to go for a morning walk every day. Rohan chose a park that was very close to a busy main road. When he walked on the side of the road, he noticed thick smoke coming out from the exhaust pipes of buses, cars and auto-rickshaws. He also saw a board showing the Air Quality Index (AQI) for that area as “Poor”. After some days, Rohan started feeling irritation in his eyes and had difficulty in breathing deeply while walking near the road.

1. (a) Which type of pollution is mainly described in this case? Answer: This case mainly describes air pollution.
2. (b) Name any two air pollutants released from vehicle exhausts. Answer: Two air pollutants are carbon monoxide (CO) and nitrogen oxides (NOx).
3. (c) What does AQI “Poor” indicate about the air quality in that area? Answer: AQI “Poor” indicates that the air is polluted and may cause breathing discomfort, especially to sensitive people.
4. (d) Suggest one change Rohan can make in his routine to protect his health. Answer: He can choose a park away from the main road or at least walk inside the park, away from traffic, where air is relatively cleaner.

A small town has a thermal power plant located near a residential colony. The power plant uses coal as fuel. Every day, tall chimneys release thick smoke into the air. The houses nearby often remain covered with a thin layer of black dust. People complain of cough, irritation in throat and black deposits on the leaves of plants in their gardens.

1. (a) Which fuel is mainly used in the thermal power plant? Answer: The thermal power plant mainly uses coal as fuel.
2. (b) Name any two air pollutants present in the smoke released from the chimneys. Answer: Sulphur dioxide (SO₂) and Suspended Particulate Matter (SPM) such as ash and soot are present.
3. (c) What simple device can be fitted in the chimneys to reduce air pollution? Answer: Filters or electrostatic precipitators can be fitted to trap harmful particles.
4. (d) Why do leaves of plants look dusty and dull near such factories? Answer: The dust and soot particles present in smoke settle on leaves, making them dusty and blocking sunlight for photosynthesis.

In a colony, some people started throwing their household garbage in an empty plot. To “clean” the plot, a few residents decided to burn all the collected garbage including plastic bags, dry leaves and other waste. Soon, a lot of thick, black smoke started spreading around the area. Nearby residents began to cough and some of them complained of a burning sensation in their eyes.

1. (a) Which type of pollution was caused mainly by burning the garbage? Answer: It mainly caused air pollution.
2. (b) Why is it especially harmful to burn plastic waste? Answer: Burning plastic releases poisonous gases and very fine particles, which can enter the lungs and harm health.
3. (c) Suggest a better method to manage garbage in the colony. Answer: Garbage should be collected separately as wet and dry waste and then composted, recycled or given to municipal waste collectors instead of burning.
4. (d) Which two health problems are mentioned in the case due to smoke? Answer: Coughing and burning/irritation in the eyes are mentioned.

To build a new residential complex near a city, a large number of trees were cut down. After a few years, residents noticed that the area had become hotter in summer and dust storms had become more common. Many people also felt that the air had become “heavy” and uncomfortable to breathe.

1. (a) Which human activity described in the case leads to air pollution? Answer: Deforestation, or cutting down a large number of trees, leads to air pollution.
2. (b) How does cutting trees affect the amount of carbon dioxide in air? Answer: Fewer trees are available to absorb carbon dioxide, so its level in the air increases.
3. (c) Why did the temperature of the area increase after trees were cut? Answer: Trees provide shade and cool the air through transpiration. Without trees, less shade and cooling occur, so the area becomes hotter.
4. (d) Suggest one step the residents can take to improve air quality again. Answer: Residents can organise tree plantation drives and grow more trees in and around the residential complex.

During winter, a metro city experiences heavy traffic on roads and people also burn wood and coal for warmth. The air becomes still and foggy. The smoke from vehicles and burning fuel mixes with fog and forms a thick, brownish layer near the ground. Schools are sometimes closed due to low visibility and many people suffer from breathing difficulty.

1. (a) What is this thick, brownish layer of polluted air called? Answer: It is called smog.
2. (b) From which two words is the term “smog” formed? Answer: “Smog” comes from the words smoke and fog.
3. (c) Mention any two harmful effects of smog described in the case. Answer: It reduces visibility (causing school closure/accidents) and causes breathing difficulty.
4. (d) Suggest one way people can help in reducing smog in winter. Answer: People can avoid burning wood/coal and reduce unnecessary vehicle use by using public transport or carpooling.

A famous marble monument is located near an industrial area. Over the years, the monument has lost its shine and yellowish patches have appeared on its surface. Scientists found that the rainwater in that area had become more acidic due to gases released from nearby factories. This acidic rain slowly reacted with the marble of the monument and damaged it.

1. (a) Which type of pollution is damaging the monument in this case? Answer: Acid rain, a result of air pollution, is damaging the monument.
2. (b) Name the two main gases that cause acid rain. Answer: Sulphur dioxide (SO₂) and nitrogen oxides (NOx) cause acid rain.
3. (c) How does acid rain affect marble structures? Answer: Acid rain reacts with marble (calcium carbonate), slowly dissolving it and causing loss of shine and surface damage.
4. (d) Suggest one step the government can take to protect such monuments. Answer: The government can control factory emissions near monuments and create a pollution-free zone around them.

A coastal town noticed that the average temperature in their area was increasing over the last few decades. Fishermen observed that some species of fish had decreased in number and that storms had become more frequent. The science teacher explained that the rise in temperature is related to global warming caused by increased greenhouse gases like carbon dioxide in the atmosphere.

1. (a) What is the name of the overall phenomenon described in this case? Answer: The phenomenon is called global warming.
2. (b) Name any two major greenhouse gases. Answer: Carbon dioxide (CO₂) and methane (CH₄) are major greenhouse gases.
3. (c) How can global warming affect sea level? Answer: Global warming melts glaciers and polar ice, causing sea level to rise.
4. (d) Mention one way in which people can help reduce global warming. Answer: People can reduce the use of fossil fuels by saving electricity and using public transport instead of private vehicles.

On “World Ozone Day”, the eco-club of a school organised a special assembly. The science teacher explained that there is a layer of ozone gas high up in the atmosphere that protects us from harmful ultraviolet (UV) rays of the Sun. She also told the students that some chemicals called CFCs used in old refrigerators and aerosol sprays can damage this ozone layer and create holes in it.

1. (a) In which part of the atmosphere is the ozone layer present? Answer: The ozone layer is present in the stratosphere.
2. (b) Why is the ozone layer important for life on Earth? Answer: It absorbs most of the harmful ultraviolet rays of the Sun and protects living beings from skin cancer and other harms.
3. (c) Name the chemical group that harms the ozone layer. Answer: Chlorofluorocarbons (CFCs) harm the ozone layer.
4. (d) How can we help in protecting the ozone layer? Answer: We can avoid using products that release CFCs, like old aerosol sprays, and support the use of CFC-free refrigerators and air-conditioners.

A river flowing near a town was once clean and full of fish. With time, many houses, shops and small factories were built along its banks. People started discharging sewage, detergents and sometimes even plastic waste into the river. Within a few years, the water turned dark and foul-smelling. Fish almost disappeared and people stopped using river water for bathing or washing clothes.

1. (a) Which type of pollution is mainly seen in this river? Answer: The river is mainly affected by water pollution.
2. (b) Name any two pollutants mentioned in the case. Answer: Sewage (wastewater) and plastic waste/detergents are the pollutants mentioned.
3. (c) Why did fish almost disappear from the river? Answer: Pollutants reduced dissolved oxygen in the water and made it toxic, so fish could not survive and died.
4. (d) Suggest one measure the town can take to improve the condition of the river. Answer: The town should treat sewage and factory waste in treatment plants before releasing them into the river and strictly ban dumping of solid waste.

A village pond, which was used by villagers for washing and cleaning, started showing a thick green layer on its surface. The villagers also used chemical fertilisers in nearby fields. After heavy rains, water from the fields flowed into the pond. The green layer of algae grew thicker and, after some time, many fish were found dead floating on the surface.

1. (a) What is the thick green layer formed on the pond called? Answer: It is called an algal bloom.
2. (b) Which substances from fertilisers caused this rapid growth of algae? Answer: Nutrients like nitrates and phosphates from fertilisers caused the rapid growth.
3. (c) Why did many fish die in the pond after some time? Answer: When algae died, decomposers used up a lot of dissolved oxygen in the water, leaving very little for fish, leading to their death.
4. (d) What is this overall process of nutrient enrichment of a water body called? Answer: This process is called eutrophication.

A small factory manufacturing coloured cloth was set up near a village. The factory discharged its coloured liquid waste into a small stream flowing through the village. After some time, villagers noticed that the colour of the stream water had changed and it gave a bad smell. Children playing in the stream developed skin rashes and itching.

1. (a) What name is given to the liquid waste discharged by factories? Answer: It is called industrial effluent.
2. (b) Name two harmful effects of such effluents on the stream. Answer: They change the colour and smell of water and make it toxic for aquatic life and unsafe for human use.
3. (c) What precaution should the factory owners take before discharging waste into the stream? Answer: They should treat the effluent in an effluent treatment plant to remove harmful chemicals before discharge.
4. (d) Why did children develop skin problems after playing in the stream? Answer: The polluted water contained harmful chemicals that irritated their skin, causing rashes and itching.

During a religious festival, many people came to a river to take a holy bath. They also immersed idols made of plaster of Paris and painted with bright colours into the river. Flowers, plastic bags and other materials were also thrown into the water. After the festival, the river bank was covered with waste and the water quality had visibly deteriorated.

1. (a) Which type of pollution increased in the river during the festival? Answer: Water pollution increased during the festival.
2. (b) Why are idols made of plaster of Paris and synthetic colours harmful for the river? Answer: Plaster of Paris and synthetic colours may contain harmful chemicals and heavy metals that dissolve in water and harm aquatic life.
3. (c) Suggest one eco-friendly alternative for idol immersion. Answer: Use small clay idols with natural colours and immerse them in specially designed artificial tanks instead of rivers.
4. (d) What can local authorities do to manage waste during such festivals? Answer: Authorities can provide dustbins, set up collection centres for idols and run awareness campaigns to keep the river clean.

A ship carrying crude oil met with an accident in the sea. Large quantities of oil leaked out and formed a thin layer on the surface of the seawater. Birds and fish living in that region were badly affected. Some sea birds were found with their feathers coated with oil, making it difficult for them to fly or float on water.

1. (a) What kind of pollution is caused by an oil spill? Answer: An oil spill causes water pollution in seas and oceans.
2. (b) How does the oil layer affect oxygen level in seawater? Answer: The oil layer reduces the exchange of gases between air and water, so less oxygen dissolves in water.
3. (c) Why do birds find it difficult to fly when their feathers are coated with oil? Answer: Oil makes their feathers heavy and sticky, reducing their ability to fly and stay warm.
4. (d) Mention one method used to control an oil spill. Answer: Oil can be removed using special floating barriers (booms) and then collected or burnt in a controlled manner.

In a village, people obtain water from a hand pump. After heavy rains, they noticed that the water became muddy and had an unusual taste. Some villagers who drank the water without boiling suffered from vomiting and diarrhoea. The health worker suggested that until the water became clear again, everyone should properly treat the water before drinking.

1. (a) What may have caused the hand pump water to become muddy? Answer: Rainwater may have carried mud and pollutants from the surface into the groundwater near the hand pump.
2. (b) Name the two diseases mentioned that villagers suffered from. Answer: They suffered from vomiting and diarrhoea.
3. (c) Suggest two simple methods the villagers can use at home to make the water safe. Answer: They can first filter the water through a clean cloth or filter and then boil it. They may also use chlorination tablets as advised.
4. (d) What do we call water that is safe for drinking? Answer: Water that is safe for drinking is called potable water.

Meera’s family installed a modern water purifier at home that uses both a filter and UV/RO technology. The purifier first passes water through a series of filters to remove suspended particles. Then it sends the water through a UV chamber and finally through a membrane that removes harmful dissolved salts and germs. The family now feels more confident about the safety of their drinking water.

1. (a) What is the main purpose of using a modern water purifier? Answer: The main purpose is to obtain safe, potable drinking water free from harmful germs and impurities.
2. (b) What is the role of filters in the purifier? Answer: Filters remove suspended impurities like dust, sand and some larger particles from water.
3. (c) Why is UV treatment used in the purifier? Answer: UV treatment kills or inactivates harmful microorganisms present in the water.
4. (d) Expand the term RO. Answer: RO stands for Reverse Osmosis.

The eco-club of a school started a campaign called “Every Drop Counts”. They surveyed the school and found many leaking taps and students leaving taps open after washing hands. Posters were put up near taps reminding everyone to close them properly. The school also collected rainwater from the roof in a tank and used it for gardening.

1. (a) What was the main aim of the campaign “Every Drop Counts”? Answer: The main aim was to save water and prevent its wastage.
2. (b) Mention two steps taken by the school to save water. Answer: They repaired leaking taps and put up posters reminding students to close taps. They also collected rainwater for gardening.
3. (c) What do we call the practice of collecting and storing rainwater for use? Answer: It is called rainwater harvesting.
4. (d) Why is it important to save clean water? Answer: Because freshwater is limited and required for drinking and daily needs; wasting it can lead to shortages in future.

In a city, a beautiful lake was surrounded by parks and walking tracks. Over the years, sewage pipes from nearby buildings got connected to drains that ended in the lake. Slowly, the lake water became dirty and foul-smelling. Foam started appearing on the surface due to detergents present in the sewage. Many fish died and people stopped visiting the lake.

1. (a) What is sewage? Answer: Sewage is wastewater from homes, offices and other buildings that contains human excreta, soaps, detergents, food waste and other impurities.
2. (b) Why did foam appear on the surface of the lake? Answer: Foam appeared due to the presence of detergents and other chemicals in the sewage.
3. (c) Suggest a measure the city should take to protect the lake. Answer: Sewage should be diverted to a sewage treatment plant and treated before disposal, not allowed to enter the lake directly.
4. (d) Why did fish die in large numbers? Answer: Decomposition of organic matter in sewage used up dissolved oxygen in the lake, leaving insufficient oxygen for fish to survive.

Students of Class 8 visited a sewage treatment plant (STP) as part of their science project. They observed that sewage first passed through screens that removed large objects like sticks and plastic bags. Then it entered a tank where heavy particles settled at the bottom. Later, air was bubbled through another tank where microorganisms decomposed the remaining organic matter. Finally, the water was treated with chlorine before being released into a nearby river.

1. (a) What is the purpose of screens in the first stage of treatment? Answer: Screens remove large solid objects like sticks, rags and plastic bags from the sewage.
2. (b) What happens in the tank where heavy particles settle at the bottom? Answer: In that tank, solids settle down as sludge, separating from the liquid part of sewage.
3. (c) Why is air bubbled through the sewage in another tank? Answer: Air provides oxygen for microorganisms, which decompose the organic matter present in the sewage.
4. (d) Why is chlorine added before releasing the treated water into the river? Answer: Chlorine kills harmful germs and disinfects the water before it is released.

At Arjun’s home, his parents instructed everyone not to throw kitchen oil, medicines, paint or plastic pieces into the sink or toilet. They explained that such substances can choke the pipes and also make it difficult to treat sewage in treatment plants. Instead, they collected used oil and medicines separately and gave them for safe disposal.

1. (a) Why should we avoid pouring kitchen oil and paint into drains? Answer: Oil and paint can stick to the walls of pipes, choking them, and they are difficult to remove during sewage treatment.
2. (b) How does responsible use of drains at home help sewage treatment plants? Answer: It reduces the amount of harmful and non-biodegradable substances entering the sewage, making treatment easier and more effective.
3. (c) Give one example of a substance that should not be thrown into toilets. Answer: Plastic pieces (e.g., wrappers, sanitary products) should not be thrown into toilets.
4. (d) What good values do Arjun’s parents show in this case? Answer: They show environmental awareness, responsibility and concern for public health and proper waste management.

A group of Class 8 students formed a club called “Environment Watchdogs”. They observed that some shopkeepers near the school were burning plastic and paper waste in the evenings, causing smoke. They politely explained to the shopkeepers how burning plastic releases harmful gases and suggested that they give their waste to the municipal collection van instead. The club also organised a street play on “Say No to Pollution” in their neighbourhood.

1. (a) Which two types of pollution can increase if shopkeepers burn waste regularly? Answer: Air pollution and, indirectly, land pollution can increase.
2. (b) Why is burning plastic waste particularly harmful? Answer: Burning plastic releases toxic gases and fine particles that harm human health and the environment.
3. (c) What alternative method of waste disposal did students suggest? Answer: They suggested giving waste to the municipal collection van for proper disposal or recycling.
4. (d) How did the students create awareness in their neighbourhood? Answer: They organised a street play on “Say No to Pollution” to educate people.