CBSE Class 12 Biology Environmental Issues Worksheet Set A

Question. Electrostatic precipitators can remove how much percentage of particutate matter present in exhaust from a thermal power plant -
(a) 90%
(b) 95%
(c) 99%
(d) 100%

Answer : C

Question. Which of the following is not associated with catalytic convertors -
(a) Conversion of unburnt hydrocarbon to CO2 & H2O
(b) Conversion of CO to CO2
(c) Conversion of NOx to N2
(d) Conversion of SO2 to S

Answer : D

Question. Motor vehicles equipped with catalytic convertor should use unleaded petrol because -
(a) Lead in petrol inactivates the catalyst
(b) Lead in petrol act as catalyst
(c) Lead in petrol start to burn along petrol
(d) Lead in petrol leads to checking burning of petrol

Answer : A

Question. Domestic sewage primarily contains -
(a) Suspended solid
(b) Colloidal matter
(c) Biodegradable matter
(d) Dissolved matter

Answer : C

Question. About highly sewage polluted water, what is true -
(a) High DO and BOD
(b) High DO and less BOD
(c) Low DO and low BOD
(d) Low DO and high BOD

Answer : D

Question. In 1990s what was the rank of Delhi among the 41 most polluted cities of the world -
(a) 1st
(b) 2nd
(c) 3rd
(d) 4th

Answer : D

Question. What was the main step taken in Delhi to control air pollution after Public interest litigation (PIL) filed in Supreme court. -
(a) Reduction in vehicles
(b) Use of CNG in buses instead of Diesel
(c) Use of catalytie convertor
(d) Plantation

Answer : B

Question. All the buses of Delhi were converted to run on CNG by The end of 2002. Why CNG is better than Diesel-
(a) CNG burns most efficiently
(b) Little of it is left unburnt
(c) Inactivate catalyst of catalytical convertor
(d) Both (a) and (b)

 Answer : D

Question. The Government of India through a new auto fuel policy has laid out a road map to cut down vehicular pollution in Indian cities. Most stringent norms for fuels means-
(a) Steadily reducing the sulphur content in petrol
(b) Steadily reducing the aromatics content in petrol
(c) Steadily reducing the sulphur and aromatics content in petrol and diesel
(d) Steadily reducing the particulated matter in petrol and Diesel

Answer : C

Question. With which polyblend was mixed to lay roads. Which show increased water repellant properties -
(a) Polysterene
(b) Bitumen
(c) Polyethylene
(d) Plastic

Answer : A

Question. e - wastes generated in developed countries, is used by developing countries for recovery of -
(a) Gold
(b) Nickel
(c) Copper
(d) All the above

Answer : D

Question. According Euro-III norms, what should be the level of sulphur in diesel and petrol respectively -
(a) 150 ppm & 350 ppm
(b) 350 ppm & 150 ppm
(c) 250 ppm & 350 ppm
(d) 350 ppm & 250 ppm

 Answer : B

Question. According to Euro-III norms, In petrol or diesel aromatic hydrocarbons are to be contained at 42 percent and goal of it to bring down the level of sulphur -
(a) 30%
(b) 40%
(c) 42%
(d) 35%

Answer : D

Ques. Global warming can be controlled by
(a) increasing deforestation, slowing down the growth of human population
(b) increasing deforestation, reducing efficiency of energy usage
(c) reducing deforestation, cutting down use of fossil fuel
(d) reducing reforestation, increasing the use of fossil fuel. 

Answer: C

Ques. Climate of the world is threatened by
(a) decreasing amount of atmospheric oxygen
(b) increasing amount of atmospheric carbon dioxide
(c) decreasing amount of atmospheric carbon dioxide
(d) increasing concentration of atmospheric oxygen. 

Answer: B

Ques. Which one of the following pairs of gases are the major cause of “greenhouse effect”?
(a) CO₂ and O₃ 
(b) CO₂ and CO
(c) CFCs and SO₂ 
(d) CO₂ and N₂O 

Answer: D

Ques. Which one of the following is correct expanded form of the acronym?
(a) IPCC = International Panel for Climate Change
(b) UNEP = United Nations Environmental Policy
(c) EPA = Environmental Pollution Agency
(d) IUCN = International Union for Conservation of Nature and Natural Resources 

Answer: D 

Ques. The two gases making highest relative contribution to the greenhouse gases are
(a) CO₂ and CH₄ 
(b) CH₄ and N₂O
(c) CFCs and N₂O
(d) CO₂ and N₂O.

Answer: A

Ques. Which one of the following is the correct percentage of the two (out of the total of 4) greenhouse gases that contribute to the total global warming?
(a) N₂O 6%, CO₂ 86%
(b) Methane 20%, N₂O 18%
(c) CFCs 14%, methane 20%
(d) CO₂ 40%, CFCs 30% 

Answer: C

Ques. Which one of the following pairs is mismatched?
(a) Fossil fuel burning – release of CO₂
(b) Nuclear power – radioactive wastes
(c) Solar energy – greenhouse effect
(d) Biomass burning – release of CO₂

Answer: C

Ques. Maximum greenhouse gas released by which of the following country?
(a) India
(b) France
(c) USA
(d) Britain 

Answer: C

Ques. If there was no CO2 in the earth’s atmosphere, the temperature of earth’s surface would be
(a) higher than the present
(b) dependent on the amount of oxygen in the atmosphere
(c) same as present
(d) less than the present. 

Answer: D

Ques. The CO2 content by volume, in the atmospheric air is about
(a) 3.34%
(b) 4%
(c) 0.0314%
(d) 0.34%. 

Answer: C

Ques. The true statement about ‘greenhouse effect’ is that it is
(a) caused by combination of many gases
(b) caused only by CO₂
(c) caused by CO₂, CFC, CH₄ and NO₂ gases
(d) none of these. 

Answer: C

Ques. Which one of the following gases contributes maximum to the ‘greenhouse effect’ on the earth?
(a) Carbon dioxide
(b) Chlorofluorocarbon
(c) Freon
(d) Methane 

Answer: A

Ques. Greenhouse effect is warming due to
(a) infra-red rays reaching earth
(b) moisture layer in atmosphere
(c) increase in temperature due to increase in carbon dioxide concentration of atmosphere
(d) ozone layer of atmosphere. 

Answer: C

Ques. Montreal protocol was signed in 1987 for control of
(a) transport of genetically modified organisms from one country to another
(b) emission of ozone depleting substances
(c) release of greenhouse gases
(d) disposal of e-wastes.

Answer: B

Ques. Snow-blindness in Antarctic region is due to
(a) freezing of fluids in the eye by low temperature
(b) inflammation of cornea due to high dose of UV-B radiation
(c) high reflection of light from snow
(d) damage to retina caused by infra-red rays.

Answer: B

Ques. Which of the following protocols did aim reducing emission of chlorofluorocarbons into atmosphere?
(a) Geneva Protocol
(b) Montreal Protocol
(c) Kyoto Protocol
(d) Gothenburg Protocol

Answer: B

Ques. Which of the following statements about ozone is correct?
(a) Tropospheric ozone protects us from UV radiations.
(b) Stratospheric ozone is ‘bad’.
(c) Tropospheric ozone is ‘good’.
(d) Stratospheric ozone protects us from UV radiations.

Answer: D

Ques. In stratosphere, which of the following elements acts as a catalyst in degradation of ozone and release of molecular oxygen?
(a) Carbon
(b) Cl
(c) Fe
(d) Oxygen 

Answer: B

Ques. World Ozone Day is celebrated on
(a) 5th June
(b) 21st April
(c) 16th September
(d) 22nd April.

Answer: C

Ques. Depletion of which gas in the atmosphere can lead to an increased incidence of skin cancers?
(a) Ammonia
(b) Methane
(c) Nitrous oxide
(d) Ozone

Answer: D

Ques. Which of the following is not one of the prime health risks associated with greater UV radiations through the atmosphere due to depletion of stratospheric ozone?
(a) Damage to eyes (b) Increased liver cancer
(c) Increased skin cancer
(d) Reduced immune system

Answer: B

Domestic sewage and industrial effluents Questions and Answers

Question. Fill the gap in the above given diagram.

Ans. 

Question. Introduction of which nutrient in water bodies result eutrophication? Choose the correct answer.
1. Nitrogen and phosphorus
2. Calcium and phosphorus
3. Calcium and nitrogen
4. Iron and calcium
Answer. Nitrogen and phosphorus

Question. Give reasons why there is a continuous increase in the DDT content in different trophic levels of the chain?

Answer. This happens because a toxic substance accumulated by an organism cannot be metabolized or excreted,and is thus passed on to the next higher trophical level.

Question. What percentage of global warming is contributed by each of the following?
i)Carbon di oxide
ii)chlorofluorocarbons
iii)nitrous oxide and
iv) methane
Answer. i)60%, ii) 14%, iii)6%, iv) 20%

Question. Ornithologists observed a decline in the bird population I the area near a lake after the setting of an industrial unit in the same area. explain the cause responsible for the decline observed?
Answer. High concentration of DDT interferes with calcium metabolism in birds and cause thinning of egg shells and their premature breaking,this eventually leads to a decline in bird population.

Environmental Issue Questions and Answers

Question. Match correctly the following and choose the correct option
i. Environment Protection Act A. 1974
ii. Air Prevention & Control of Pollution Act B. 1987
iii. W ater Act C. 1986
iv. Amendment of Air Act to include noise D. 1981
The correct matches is;
a. i-C, ii-D, iii-A, iv-B b. i-A, ii-C, iii-B, iv-D
c. i-D, ii-A, iii-B, iv-C d. I-C, ii-D, iii-B, iv-A
Answer. A

Question. In the textbook you came across Three Mile Island and Chernobyl disasters associated with accidental leakage of radioactive wastes. In India we had Bhopal gas tragedy. It is associated with which of the following?
a. CO2 b. Methyl Iso-Cyanate
c. CFC’s d. Methyl Cyanate
Answer. B

Question. Blends of polyblend and bitumen, when used, help to increase road life by a three times. What is the reason?
Answer. Water resistant; non biodegradable; long lasting

Question. Why has the National Forest Commission of India recommended a relatively larger forest cover for hills than for plains?
Answer. Control soil erosion and land sliding

Question. Name the Industry which causes air, soil and water pollution.
Answer. Fertilizer Industry.

Short Answer Questions

Question. How have human activities caused desertification? Explain. 
Answer. Human activities like over-cultivation, unrestricted grazing, deforestation and poor irrigation practices result in arid patches of land. The fertile top soil that may take centuries to develop is eroded due to these activities. When large barren patches extend and meet over time, a desert is created. Increased urbanisation is also one of the causes of desertification.

Question. “Determination of Biological Oxygen Demand (BOD) can help in suggesting the quality of a water body.” Explain. 
Answer. High BOD of a water body indicates growth of more number of micro-organisms in water. This results in bad quality of water. Bad water quality will lead to death of aquatic creatures and hence more polluting potential. Whereas lower BOD of water body indicates less number of microorganisms in water. There is good quality of water in which aquatic life flourishes and there is less polluting potential.
The amount of oxygen required for microbial breakdown of biodegradable organic matter is called BOD.

Question. Lower BOD of a water body helps reappearance of clean-water organisms. Explain.
Answer. Lowering of Biological Oxygen Demand (BOD) results in decreased biodegradable material in the water body. This results in reduced microbial decomposition. When there is no decomposition,oxygen utilisation is reduced and there is more Dissolved Oxygen (DO) available. Thus, clean water-organisms reappear.

Question. Thermal power plants are inevitable in an industrial and densely populated country like ours.
What harm do they do to the environment? Also mention any precaution that could be taken to save our environment.
Answer. The particulate and gaseous pollutants are released from thermal power plants which lead to harmful effects. These pollutants can cause:
(i) breathing or respiratory symptoms when inhaled.
(ii) irritation, inflammations and damage to lungs and premature death.
Precautionary measures include use of electrostatic precipitators by which 99% of the particulate matters can be removed from the exhaust.

Question. A person has inhaled air having particulate pollutants of size less than 2.5 micrometers in diameter. What could be the impact of their pollutants on his respiratory system? 
Answer. Particulate pollutants inhaled deep into the lungs cause irritation, inflammation, damage to the lungs, and premature death.

Question. List four benefits to human life by eliminating the use of CFCs.
Answer. (i) Delay in aging of skin (ii) Prevent damage to skin cells
(iii) Prevent skin cancer (iv) Prevent snow blindness or inflammation of cornea
(v) Prevent cataract (vi) Prevents ozone depletion
(vii) Prevents global warming (viii) Reduces greenhouse effect
(ix) Reduces odd climatic changes or El Nino effect. 

Question. Suppose sewage water is disposed off in the river. What will be its effect on BOD and dissolved oxygen?
OR
Sewage discharge into clean water body leads to increased fish mortality. Explain.
Answer. Discharge of sewage water into a river will increase nutrients and thereby promotes algal growth. This will result in rise of BOD (Biochemical Oxygen Demand) as decomposers will consume more dissolved oxygen in river. If sewage quantity is large, the whole of the dissolved oxygen will be consumed leaving nothing for respiration of fishes and other aquatic organisms. This increases the mortality rate of aquatic creatures.

Question. Explain the causes of global warming. Why is it a warning to mankind?
Answer. The gradual continuous increase in average temperature of surface of the Earth as a result of increase in concentration of greenhouse gases is termed as global warming.
(i) Cause
- Increase in the level of greenhouse gases (CO₂, methane, etc.) in the atmosphere.
These gases allow the heat waves to reach earth but prevent their escape and thus the earth becomes warm.
(ii) Effects
- The temperature of the earth has increased by 0.6°C in the last three decades, which will lead to changes in precipitation patterns.
- Rise in temperature leads to deleterious changes in environment resulting in odd climatic changes called El Nino effect.
- The rise in temperature will lead to the increased melting of polar ice caps which will cause the rise in sea level and many coastal areas will be submerged.
- Increased temperature will lead to increased weed growth, eruption of diseases and pests. Thus,crop productivity will decrease.
(iii) Control of global warming
- Global warming can be controlled by:
(a) Reducing deforestation
(b) Planting trees (afforestation)
(c) Slowing down the growth of human population
(d) Reduction of emission of greenhouse gases into the atmosphere
(e) Cutting down use of fossil fuels
(f) Improving efficiency of energy usage.
(g) International initiatives requited to reduce emission of greenhouse gases into atmosphere

Long Answer Questions

Question. Mention the major cause of air pollution in metro cities. Write any three ways by which it can be reduced. 
Answer. Major causes of air pollution are: 
(a) Smoke from forest fires, volcanic eruptions, etc.
(b) Decomposition of garbage resulting in release of unwanted gases into the atmosphere.
(c) Burning of fossil fuels in automobiles and industries release particulate and air pollutants.
(d) Use of leaded petrol.
(e) Gaseous wastes or particulate matter as by-products of various industries.
(f) Smoke stacks of thermal power plants, smelters and other industrial release, particulate and gaseous air pollutants with harmless gases like N2, O2, etc.
Control methods:
(i) Using electrostatic precipitators to remove particulate matter from exhaust of industries and thermal power plant.
(ii) Using scrubber to remove gases like SO₂.
(iii) Use of catalytic converters in automobiles for reducing emission of poisonous gases.

Question. Explain biomagnification. How does biomagnification of DDT affect the population of fisheating birds?
Answer. Unknowingly some harmful chemicals enter our bodies through the food chain. We use several pesticides and other chemicals to protect our crops from diseases and pests. These chemicals are either washed down into the soil or into the water bodies. From the soil, these are absorbed by the plants along with water and minerals, and from the water bodies these are taken up by aquatic plants and animals. This is one of the ways in which they enter the food chain. As these chemicals are not degradable, these get accumulated progressively at each trophic level. As human beings occupy the topmost level in any food chain, the maximum concentration of these chemicals get accumulated in our bodies. This phenomenon is known as biological magnification. The population of fish-eating birds living on the bank of a contaminated lake differs from those living on the bank of another lake free from such insecticides (DDT). DDT being highly poisonous caused the thinning of their egg-shells and population of birds declined. The phenomenon is known as biological magnification.

Question. What is global warming? List four strategies for reducing global warming.
Answer. Increase in the level of greenhouse gases in the atmosphere causes rise in global mean temperature called global warming.
Four strategies for reducing global warming are:
Control of global warming
- Global warming can be controlled by:
(a) Reducing deforestation
(b) Planting trees (afforestation)
(c) Slowing down the growth of human population
(d) Reduction of emission of greenhouse gases into the atmosphere
(e) Cutting down use of fossil fuels
(f) Improving efficiency of energy usage.
(g) International initiatives requited to reduce emission of greenhouse gases into atmosphere.

Question. (a) What depletes ozone in the stratosphere? How does this affect human life?
(b) Explain biomagnification of DDT in an aquatic food chain. How does it affect the bird population?
Answer. (a) Chlorofluorocarbons (CFCs) deplete ozone in the stratosphere.
UV(B) damages DNA causing mutation, skin cancer, inflammation of cornea, cataract, aging of skin, snow blindness.
(b) If DDT reaches from the agricultural field, it gets into the water body (the concentration is 0.0003 ppm) and enters the food chain: zooplanktons (0.04 ppm) → small fish (0.05 ppm) → large fish (2 ppm) → any fish eating bird (5 ppm). Concentration of DDT increases along the food chain, reaching a high level in the top carnivore bird.
DDT concentration disturbs Ca++ metabolism, egg shells become thin, premature breaking resulting in decline in bird population.

Question. Explain the ways by which solid waste can be disposed.
Answer.(i) Open burning: Municipal waste is reduced by burning in open dumps but the unburnt waste serve as the breeding ground for rats and flies.
(ii) Sanitary landfills: Wastes are dumped in a depression or trench after compaction and covered with dirt. But seepage of chemicals from these landfills can pollute underground water resources. Landfills are also getting filled.
(iii) Rag-pickers and kabadiwallahs: Wastes are collected and separated out into reusable or recyclable categories.
(iv) Natural breakdown: The biodegradable materials are kept into deep pits in the ground for natural breakdown.
(v) Recycling: E-wastes can be recycled in specifically built factories or manually to recover important metals like copper, iron, silicon, nickel and gold but in eco-friendly manner. Recycling in developing countries involve manual participation, exposing workers to toxic substances present in e-waste.
(vi) Incineration: Majority of e-wastes generated in developed world is exported to developing world (mainly China, India, Pakistan) where they are incinerated. Incinerators are crucial for disposal of hospital wastes.

Question. (a) What is El Nino effect? Explain how it accounts for biodiversity loss.
(b) Explain any three measures that you as an individual would take, to reduce environmental pollution. 
Answer. (a) El Nino effect refers to the odd climatic changes in pacific ocean due to rise in temperature.It leads to increased melting of polar ice caps as well as other places like the Himalayan snow caps. This will result in a rise in sea level that can submerge many coastal areas. Thus, resulting in biodiversity loss, it can also result in intense storms in some places and droughts or more rains in others.
(b) Measures to reduce environmental pollution
(i) Use of renewable energy resources.
(ii) Use of television and other gadgets at low pitch.
(iii) Minimum use of fossil fuel.
(iv) No tobacco smoking.
(v) Planting more trees

Question. Mention the six harmful effects of noise on human health.
Answer. Six harmful effects of noise on human population are:
Harmful effects (Psychological and Physiological disorders)
(a) Sleeplessness (b) Stress
(c) Increased rate of heartbeat and hypertension
(d) Breathing problems
(e) Damage of ear drums impairing hearing ability permanently (by the sound of jet plane/rocket or chronic exposure to sound).
(f) Gastric problems—nausea
(g) Emotional disturbance

Question. (a) State the cause of depletion of ozone layer.
(b) Specify any two ill-effects that it can cause in the human body.
Answer. (a) UV radiations act upon CFCs (chlorofluorocarbons) releasing Cl atoms in the stratosphere.
These Cl atoms combine with O₃ and degrade it.
(b) Ill-effects of ozone depletion:
(i) UV-B damages DNA and proteins of living organisms causing mutation.
(ii) It causes skin aging, skin cell damage and skin cancers.
(iii) UV-B is absorbed by human eye and at high dose it causes inflammation of cornea. This is called snow-blindness cataract.

Question. With the help of a flow-chart exhibit the events of eutrophication. 
Answer. Water in young lake is cold and clear to support life.
                                         ↓
With time, water is enriched with nutrients such as nitrogen and phosphorus by streams draining into it.
                                         ↓
As lake’s fertility increases, plant and animal life increase/proliferates.
                                         ↓
Organic matter begins to deposit at the bottom of the lake. Silt and organic debris pile up and makes the lake shallower and warmer.
                                         ↓
Marsh plants develop roots and begin to fill the original lake basin
                                         ↓
Eventually the lake gives way to large masses of floating plants finally converting it into land.
(Natural aging)

Question. A plastic sack manufacturer in Bengaluru, Ahmed Khan has managed to find an ideal solution to the problem of plastic waste. Explain in five steps the efforts of Ahmed Khan to meet the challenges of solid waste management.
Answer. (i) Ahmed Khan developed polyblend, which is a fine powder of recycled modified plastic.
(ii) Polyblend is mixed with bitumen and used to lay roads. This work is done in collaboration with R V engineering college and Bangalore city corporation.
(iii) Polyblend enhanced water-repellant property of bitumen and increase the road life.
(iv) Khan offered a price to rag pickers which enhanced their income and improved their livelihood.
(v) Thus solid waste management was achieved by removal and proper disposal of plastic waste from the city.

Question. What is eutrophication? How does a lake undergo accelerated eutrophication?
Answer. Eutrophication
- It is defined as the natural aging of a lake by biological enrichment of its water.
- Water in a young lake is cold and clear to support life.
- With time, it is enriched with nutrients like nitrogen and phosphorus by streams draining into it.
- This encourages growth of aquatic life—plant and animal life.
- Organic remains deposit at the bottom of the lake and with time makes the water warmer and shallower.
- Marsh plants take root in the shallows and begin to fill in original lake basin.
- Eventually, floating plants develop in the lake, finally converting it into land.
- According to climate, size of the lake and other factors, natural ageing of lake may span up to thousands of years.
- The accelerated aging of lakes due to sewage, agricultural and industrial wastes is called cultural or accelerated eutrophication.
- Prime contaminants are nitrates and phosphates (plant nutrients) that overstimulate algal growth. This causes unsightly scum, unpleasant odour, etc. Which depletes the amount of dissolved oxygen. Other pollutant may also poison fish, whose decomposing remains further depletes the dissolved O2 and thus choke a lake to death.
Heated (thermal) waste waters flowing out of electricity generating units like thermal power plants also act as pollutants.

Effect: (i) Eliminate or reduce number of organisms sensitive to high temperature.
(ii) Enhance growth of plant and fish in extremely cold areas.
(iii) Cause damage to indigenous flora and fauna.

Question. (a) Expand BOD.
(b) At a particular segment of a river near a sugar factory, the BOD is much higher than the normal level. What is it indicative of? What will happen to the living organisms in this part of the river?
(c) Under what conditions will the BOD be lowered in the river? How will it affect the aquatic life?
Answer. (a) BOD—Biochemical Oxygen Demand
(b) It indicates the addition of lot of organic matter; microorganisms involved in the biodegradation of organic matter in the water body consume a lot of oxygen and as a result, there is a sharp decline in the dissolved oxygen content, downstream from the point of addition of effluent from the factory. This causes mortality of fish and other aquatic organisms.
(c) When the amount of organic matter decreases and the microbes do not need oxygen for decomposition, the BOD decreases. Thus, aquatic organisms will start flourishing.

 QUESTION

1 BOD of two samples of water A and B were 120mg/L and 400mg/L respectively. Which sample is more polluted?

2 Name the world’s most problematic aquatic weed. What is the nature of the water body in which the weeds grow abundantly?

3 Between amphibians and birds, which will be able to cope with global warming? Give reason.

6 It has been recorded that the temperature of the earth’s atmosphere has increased by 0.6oC.

a) What has caused this increase?

b) Explain its consequences.

7 DDT content in the water of a lake that supplies drinking water to the near by villages, is found to be 0.003ppm.The kingfishers of that area are reported to have 2ppm of DDT. Why has the concentration increased in these birds? What harm will this cause to the bird population? Name the phenomenon.

8 How do automobiles fitted with catalytic converters reduce air pollution? Suggest the best fuel for such vehicles.

9 Explain accelerated eutrophication. Mention any two consequences of this phenomenon.

10 A crane has DDT level as 5ppm in its body. What would happen to the population of such bird? Explain giving reasons. 

11 Explain the causes of algal bloom in a water body. How does it affect an ecosystem?

12 A factory drains its waste water into the nearby lake. It has caused algal bloom. a) How was the algal bloom caused? b) What would be the consequences? c) Name the phenomenon that caused it. 

14 Explain the causes of global warming. Why is it a warning to mankind?

15 Explain any three measures which will control vehicular air pollution in Indian cities.

16 Particulate and gaseous pollutants along with harmless gases are released from the thermal power plants.

i) Name any two harmless gases released.

ii) Name the most widely used device of removing particulate pollutants from the air. Explain how the device is used.