Pollution, environmental laws and green technology: previous-year questions
73 real UPSC Prelims questions (2011–2026) with the official answer and a clear explanation. 25 of them came in the last five papers.
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Questions per year, counted from the official papers.
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There is some concern regarding the nanoparticles of some chemical elements that are used by the industry in the manufacture of various products. Why?
- 1. They can accumulate in the environment, and contaminate water and soil.
- 2. They can enter the food chains.
- 3. They can trigger the production of free radicals.
Select the correct answer using the code given below.
Answer (d) & explanation
All three are real concerns (d). Because they are so tiny, nanoparticles of silver, titanium dioxide and zinc oxide pass easily into soil, water and living cells, so they can accumulate and contaminate the environment (1). They can move up food chains (2). They can also trigger free radicals that cause oxidative damage to cells (3).
Their small size gives them a huge surface area, which makes them useful in sunscreens, medicines and electronics but also more reactive. Notice how the same property that makes a technology useful can make it risky, the core idea of the precautionary principle.
Answer as per the official UPSC answer key.
Acid rain is caused by the pollution of environment by
Answer (d) & explanation
Nitrous oxide and sulphur dioxide is correct (d), read as nitrogen oxides and sulphur dioxide. Sulphur dioxide, mainly from burning coal, and nitrogen oxides, from vehicles and power plants, react with water vapour and oxygen to form sulphuric and nitric acids, which fall as acid rain with pH below 5.6. (a) is wrong: nitrogen gas is inert, and CO₂ forms only weak carbonic acid. (b) is wrong: carbon monoxide does not cause acid rain. (c) is wrong: ozone is not an acid former.
Notice the effects: acid rain damages forests, acidifies lakes and erodes marble, as feared for the Taj Mahal from the Mathura refinery; the Taj Trapezium Zone was created to protect it. Flue gas desulphurisation cuts SO₂. Trap: the option's 'nitrous oxide' is loose wording for NOx.
Answer as per the official UPSC answer key.
Photochemical smog is a resultant of the reaction among
Answer (a) & explanation
Option (a) is correct. Photochemical smog, the Los Angeles type, forms when sunlight acts on nitrogen oxides and hydrocarbons from vehicle exhaust. The reactions produce ozone and peroxyacetyl nitrate (PAN), which irritate eyes and lungs and damage plants; the brown haze includes NO₂. So the mixture of NO₂, O₃ and PAN in sunlight describes it best. (b) is wrong: carbon monoxide and oxygen are not its key components. (c) is wrong: it forms in warm, sunny conditions, not low temperatures. (d) is wrong: it peaks in the afternoon, not evening.
Notice the contrast: classical or London smog (1952) is sulphur dioxide plus smoke and fog in cold, damp weather. Delhi's winter smog mixes both types with stubble smoke. Trap: (a) lists products of the reaction, which UPSC accepts.
Answer as per the official UPSC answer key.
Which of the following can be found as pollutants in the drinking water in some parts of India?
- 1. Arsenic
- 2. Sorbitol
- 3. Fluoride
- 4. Formaldehyde
- 5. Uranium
Select the correct answer using the codes given below.
Answer (c) & explanation
Arsenic, fluoride and uranium are correct (c). Indian groundwater is contaminated with arsenic in the Ganga–Brahmaputra plains of West Bengal, Bihar, UP and Assam (1), fluoride in Rajasthan, Andhra Pradesh, Telangana and other states (3), and uranium in Punjab, Rajasthan and elsewhere (5). Item 2 is wrong: sorbitol is a sugar substitute. Item 4 is wrong: formaldehyde is an industrial chemical and preservative, not a known drinking-water contaminant here. So (a), (b) and (d) fail.
Notice the data: the CGWB's 2024 report found uranium above safe limits in parts of Punjab and nitrate in many districts. The Jal Jeevan Mission treats such water through community plants. Fluoride causes fluorosis, arsenic causes skin lesions and cancer. Trap: lab-sounding names are not always pollutants.
Answer as per the official UPSC answer key.
Due to improper/indiscriminate disposal of old and used computers or their parts, which of the following are released into the environment as e-waste?
- 1. Beryllium
- 2. Cadmium
- 3. Chromium
- 4. Heptachlor
- 5. Mercury
- 6. Lead
- 7. Plutonium
Select the correct answer using the codes given below.
Answer (b) & explanation
Items 1, 2, 3, 5 and 6 are correct (b). Computers contain beryllium in connectors and motherboards (1), cadmium in batteries and chips (2), hexavalent chromium used against corrosion (3), mercury in switches and older flat screens (5), and lead in solder and old CRT glass (6). Item 4 is wrong: heptachlor is an organochlorine insecticide, not part of electronics. Item 7 is wrong: plutonium is a nuclear material and is not used in computers. So (a), (c) and (d) fail.
Notice India's rules: the E-Waste (Management) Rules, 2022 use Extended Producer Responsibility with tradable EPR certificates. India produced over 1.7 million tonnes of e-waste in 2023–24, and much is handled informally in places like Seelampur, Delhi. Trap: scary-sounding toxins are not all e-waste.
Answer as per the official UPSC answer key.
The National Green Tribunal Act, 2010 was enacted in consonance with which of the following provisions of the Constitution of India?
- 1. Right to healthy environment, construed as a part of Right to life under Article 21
- 2. Provision of grants for raising the level of administration in the Scheduled Areas for the welfare of Scheduled Tribes under Article 275(1)
- 3. Powers and functions of Gram Sabha as mentioned under Article 243(A)
Select the correct answer using the codes given below :
Answer (a) & explanation
Statement 1 only is correct (a). The NGT Act, 2010 preamble says the right to a healthy environment is part of the right to life under Article 21, and that the Act gives effect to India's commitments at the 1992 Rio Earth Summit. (2) is wrong: Article 275(1) provides grants to states for tribal welfare and Scheduled Areas; it has nothing to do with the tribunal. (3) is wrong: Article 243A concerns the Gram Sabha's powers. So (b), (c) and (d) fail.
Notice the tribunal: the NGT's principal bench is in New Delhi, with zonal benches at Bhopal, Pune, Kolkata and Chennai. It must decide cases within six months, follows the polluter pays and precautionary principles, and appeals go to the Supreme Court. India was the third country, after Australia and New Zealand, with such a body.
Answer as per the official UPSC answer key.
Lead, ingested or inhaled, is a health hazard. After the addition of lead to petrol has been banned, what still are the sources of lead poisoning?
- 1. Smelting units
- 2. Pens and pencils
- 3. Paints
- 4. Hair oils and cosmetics
Select the correct answer using the codes given below :
Answer (b) & explanation
Smelting units and paints are correct per UPSC's key (b), but the key is doubtful on item 4. Lead still comes from smelters and battery-recycling units (1) and from lead-based paints (3). Item 2 is wrong: 'pencil lead' is actually graphite mixed with clay. Item 4 is the doubt: some traditional cosmetics such as sindoor, surma/kohl and certain hair dyes have been found to contain lead, so (a)-type answers including 4 are arguable; UPSC left them out. So (c) fails on any reading.
Notice the rules: India's 2016 rules cap lead in household paint at 90 ppm. A 2020 UNICEF report estimated about 27.5 crore Indian children have high blood lead. Trap: the word 'lead' in pencils.
Answer as per the official UPSC answer key.
Consider the following statements :
Chlorofluorocarbons, known as ozone-depleting substances, are used
- 1. in the production of plastic foams
- 2. in the production of tubeless tyres
- 3. in cleaning certain electronic components
- 4. as pressurizing agents in aerosol cans
Which of the statements given above is/are correct?
Answer (c) & explanation
Statements 1, 3 and 4 are correct (c). Chlorofluorocarbons were used as blowing agents for plastic foams (1), as solvents to clean electronic circuit boards (3), as aerosol propellants (4) and as refrigerants. Statement 2 is wrong: CFCs are not used to make tubeless tyres. So (a), (b) and (d) fail.
Notice the treaties: the Vienna Convention (1985) and Montreal Protocol (1987) phased out CFCs, and the Kigali Amendment (2016) now phases down their substitutes, HFCs, which are powerful greenhouse gases; India must cut HFCs from 2032. The ozone hole over Antarctica is expected to heal by about 2066. World Ozone Day is 16 September. Trap: tyres sound industrial but have no CFC link.
Answer as per the official UPSC answer key.
In the Union Budget 2011-12, a full exemption from the basic customs duty was extended to the bio-based asphalt (bioasphalt). What is the importance of this material ?
- 1. Unlike traditional asphalt, bioasphalt is not based on fossil fuels.
- 2. Bioasphalt can be made from non-renewable resources.
- 3. Bioasphalt can be made from organic waste materials.
- 4. It is eco-friendly to use bioasphalt for surfacing of the roads.
Which of the statements given above are correct ?
Answer (b) & explanation
Statements 1, 3 and 4 are correct (b). Bioasphalt is a road binder made from renewable plant matter such as sugar, molasses, vegetable oils, starch and lignin, or from organic waste, instead of petroleum bitumen. So it is not based on fossil fuels (1), can come from waste (3), and is eco-friendly for surfacing roads because it cuts fossil fuel use and emissions (4). Statement 2 is the trap: bioasphalt is made from renewable, not non-renewable, resources. So options (a), (c) and (d) fail.
Notice the wider idea: India pushes waste-to-road technology too, such as plastic waste roads (pioneered by R. Vasudevan) and lignin-based bio-bitumen developed by CSIR. Trap: one word, 'non-renewable', flips statement 2.
Answer as per the official UPSC answer key.
Consider the following :
- 1. Carbon dioxide
- 2. Oxides of Nitrogen
- 3. Oxides of Sulphur
Which of the above is/are the emission/emissions from coal combustion at thermal power plants ?
Answer (d) & explanation
All three are emitted (d). Burning coal in a thermal power plant releases carbon dioxide from its carbon (1). Indian coal contains some sulphur, which burns to sulphur dioxide (3). At the high furnace temperature, nitrogen and oxygen in the air combine to form nitrogen oxides (2). Coal plants also emit fly ash, particulate matter and mercury. So options (a), (b) and (c) leave out real emissions.
Notice the control side: flue gas desulphurisation (FGD) units remove SO₂, low-NOx burners cut nitrogen oxides, and electrostatic precipitators trap fly ash. India's 2015 emission norms required FGD, but the July 2025 notification exempted most Category C plants (about 78%). Coal still supplies over 70% of India's electricity, and India's net-zero target is 2070. Trap: NOx comes from the air, not the coal, but it is still a coal-combustion emission.
Answer as per the official UPSC answer key.
The formation of ozone hole in the Antarctic region has been a cause of concern. What could be the reason for the formation of this hole ?
Answer (b) & explanation
The answer is (b). In the Antarctic winter, a strong polar vortex (polar front) isolates very cold air over the continent. Temperatures fall below about −78°C, and polar stratospheric clouds form. On the ice crystals of these clouds, chlorine compounds from chlorofluorocarbons are turned into active forms. When sunlight returns in spring (September-October), this chlorine destroys ozone rapidly, creating the ozone hole. Option (a) is wrong because the process is stratospheric, not tropospheric. Option (c) is wrong because it says polar front and clouds are absent. Option (d) is wrong because warming is not the cause.
Notice the outcome: the Montreal Protocol (1987) phased out CFCs, and the ozone layer is expected to recover to 1980 levels over Antarctica by about 2066, according to UNEP-WMO assessments. The Arctic sees smaller holes because its vortex is weaker. Trap: stratosphere, not troposphere.
Answer as per the official UPSC answer key.
There is a concern over the increase in harmful algal blooms in the seawaters of India. What could be the causative factors for this phenomenon ?
- 1. Discharge of nutrients from the estuaries.
- 2. Run-off from the land during the monsoon.
- 3. Upwelling in the seas.
Select the correct answer from the codes given below :
Answer (d) & explanation
All three are correct (d). Harmful algal blooms grow when seawater gets extra nutrients, mainly nitrogen and phosphorus. Estuaries discharge sewage and fertiliser-laden river water into the sea (1). Monsoon run-off washes soil and fertilisers off the land (2). Upwelling brings cold, nutrient-rich deep water to the sunlit surface (3), as off the Kerala coast in the monsoon. So options (a), (b) and (c) leave out real causes.
Notice the wider idea: this process is eutrophication. Blooms such as Noctiluca in the Arabian Sea can create oxygen-poor dead zones and fish kills, and some algae release toxins. Warming seas make blooms more frequent. Trap: upwelling is natural, yet it is still a nutrient source.
Answer as per the official UPSC answer key.
Recently, “oilzapper” was in the news. What is it ?
Answer (a) & explanation
Option (a) is correct. Oilzapper is a consortium of oil-eating bacteria developed by TERI with Indian Oil. It is used for bioremediation: the microbes feed on oily sludge and spilled crude and break the hydrocarbons into harmless carbon dioxide and water. (b) is wrong: it is not an exploration technology. (c) is wrong: it is not a GM maize. (d) is wrong: it does not fight oil-well fires.
Notice the related product: Oilivorous-S, a TERI variant that also degrades high-sulphur crude. Bioremediation is cheaper and greener than burning or landfilling sludge, and India's Central Pollution Control Board approves such methods for refinery waste. Trap: the word 'zapper' suggests fire or blasting, not bacteria.
Answer as per the official UPSC answer key.