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.
How often UPSC asks this
Questions per year, counted from the official papers.
Attempt the questions
Newest papers first. Tap an option; the answer and the reason appear instantly.
In the context of WHO Air Quality Guidelines, consider the following statements :
- 1. The 24-hour mean of PM2·5 should not exceed 15 µg/m3 and annual mean of PM2·5 should not exceed 5 µg/m3.
- 2. In a year, the highest levels of ozone pollution occur during the periods of inclement weather.
- 3. PM10 can penetrate the lung barrier and enter the bloodstream.
- 4. Excessive ozone in the air can trigger asthma.
Which of the statements given above are correct ?
Answer (b) & explanation
Statements 1 and 4 are correct (b). Statement 1 is right: the 2021 WHO Air Quality Guidelines set PM2.5 at 15 µg/m³ for the 24-hour mean and 5 µg/m³ for the annual mean. Statement 2 is wrong: ground-level ozone forms when sunlight acts on pollutants, so it peaks in hot, sunny weather, not in bad weather. Statement 3 is wrong: PM2.5, not PM10, is fine enough to pass the lung barrier into the bloodstream. Statement 4 is right: excess ozone irritates airways and can trigger asthma.
Notice that India's National Ambient Air Quality Standards (2009) are much looser: PM2.5 at 60 (24-hour) and 40 (annual). The National Clean Air Programme (2019) targets cuts in 131 cities.
PM10 reaches the lungs, but the bloodstream needs the finer PM2.5.
Answer as per the official UPSC answer key.
With reference to polyethylene terephthalate, the use of which is so widespread in our daily lives, consider the following statements :
- 1. Its fibres can be blended with wool and cotton fibres to reinforce their properties.
- 2. Containers made of it can be used to store any alcoholic beverage.
- 3. Bottles made of it can be recycled into other products.
- 4. Articles made of it can be easily disposed of by incineration without causing greenhouse gas emissions.
Which of the statements given above are correct ?
Answer (a) & explanation
Statements 1 and 3 are correct (a). Polyethylene terephthalate (PET) is the plastic of water and soft-drink bottles. Statement 1 is right: as a fibre it is polyester, often blended with cotton and wool to add strength and resist creasing. Statement 3 is right: PET bottles are widely recycled into fibre, carpets and new bottles. Statement 2 is wrong: it is not suited to storing every alcoholic drink; long storage of strong spirits can draw out chemicals. Statement 4 is wrong: burning PET releases CO₂ and other pollutants.
Notice that India recycles a high share of its PET bottles, much of it into polyester fibre. The Plastic Waste Management Rules (amended 2022) ban many single-use plastics and set EPR targets for producers.
Answer as per the official UPSC answer key.
Which one of the following has been constituted under the Environment (Protection) Act, 1986 ?
Answer (c) & explanation
The Central Ground Water Authority was set up under the Environment (Protection) Act (c). The Central Ground Water Authority came in 1997 under Section 3(3) of the Environment (Protection) Act, 1986, after a Supreme Court order, to regulate and control groundwater use. It issues No Objection Certificates for drawing groundwater and notifies over-exploited areas. Option (a) is wrong: the Central Water Commission dates from 1945 and is an attached office under the Jal Shakti Ministry. Option (b) is wrong: the Central Ground Water Board is a survey and research body. Option (d) is wrong: the National Water Development Agency (1982) is a society that plans river linking.
Notice that India is the world's largest user of groundwater, which is why the Atal Bhujal Yojana targets falling water tables.
CGWB and CGWA sound alike. The Board studies groundwater; the Authority regulates it.
Answer as per the official UPSC answer key.
Consider the following statements :
- 1. Other than those made by humans, nanoparticles do not exist in nature.
- 2. Nanoparticles of some metallic oxides are used in the manufacture of some cosmetics.
- 3. Nanoparticles of some commercial products which enter the environment are unsafe for humans.
Which of the statements given above is/are correct ?
Answer (d) & explanation
Statements 2 and 3 are correct (d). Statement 2 is right: nanoparticles of zinc oxide and titanium dioxide are used in sunscreens, creams and other cosmetics, because they block UV rays without leaving a white layer. Statement 3 is right: some engineered nanoparticles that enter the air, water or soil can be unsafe: their tiny size lets them reach deep into the lungs, cross cell walls and harm tissues. Statement 1 is wrong: nanoparticles occur in nature, in volcanic ash, sea spray, desert dust and smoke from forest fires.
Notice the scale: a nanometre is a billionth of a metre, and nanoparticles are 1–100 nm across. At that size materials behave differently: gold looks red, and silver nanoparticles kill microbes.
Answer as per the official UPSC answer key.
Consider the following :
- 1. Carbon monoxide
- 2. Nitrogen oxide
- 3. Ozone
- 4. Sulphur dioxide
Excess of which of the above in the environment is/are cause(s) of acid rain ?
Answer (b) & explanation
Nitrogen oxides and sulphur dioxide cause acid rain (b). Sulphur dioxide (SO₂), mostly from burning coal and oil, and nitrogen oxides (NOₓ), mostly from vehicles and power plants, react with water in the air to form sulphuric and nitric acids. These fall as acid rain, with a pH below about 5.6. Item 1 is wrong: carbon monoxide is a poisonous gas but does not make rain acidic. Item 3 is wrong: ozone at ground level is a harmful smog pollutant, but it is not an acid-forming gas. So options (a), (c) and (d) fall.
Notice the famous Indian case: the yellowing of the Taj Mahal was blamed partly on SO₂ from the Mathura refinery, which led to the Taj Trapezium Zone.
Answer as per the official UPSC answer key.
Why is there a concern about copper smelting plants?
- 1. They may release lethal quantities of carbon monoxide into environment.
- 2. The copper slag can cause the leaching of some heavy metals into environment.
- 3. They may release sulphur dioxide as a pollutant.
Select the correct answer using the code given below.
Answer (b) & explanation
Slag leaching and sulphur dioxide are the concerns (b). Statement 2 is right: the leftover copper slag can leach heavy metals such as arsenic and lead into soil and water. Statement 3 is right: most copper ores are sulphides, so smelting gives off sulphur dioxide, which causes acid rain and breathing problems. Statement 1 is wrong: carbon monoxide is not a major pollutant from copper smelters; it comes mostly from incomplete burning in vehicles.
Notice the Sterlite copper plant at Thoothukudi, Tamil Nadu, which was closed in 2018 after protests in which 13 people were killed in police firing. The Supreme Court upheld the closure in 2024. Smelters often capture SO₂ to make sulphuric acid.
Answer as per the official UPSC answer key.
With reference to furnace oil, consider the following statements :
- 1. It is a product of oil refineries.
- 2. Some industries use it to generate power.
- 3. Its use causes sulphur emissions into environment.
Which of the statements given above are correct?
Answer (d) & explanation
All three statements are correct (d). Statement 1 is right: furnace oil is a heavy, dark fuel left after the lighter fractions, such as petrol and diesel, are taken out at an oil refinery. Statement 2 is right: factories burn it in boilers, furnaces and generators to make heat and power. Statement 3 is right: it is high in sulphur, so burning it releases sulphur dioxide.
Notice that the Supreme Court banned furnace oil and pet coke in Delhi-NCR in 2017 to fight air pollution. Ships face similar limits: the IMO 2020 rule cut sulphur in marine fuel to 0.5%. India moved to BS-VI fuel in 2020, with sulphur limited to 10 ppm.
Answer as per the official UPSC answer key.
Magnetite particles, suspected to cause neurodegenerative problems, are generated as environmental pollutants from which of the following?
- 1. Brakes of motor vehicles
- 2. Engines of motor vehicles
- 3. Microwave stoves within homes
- 4. Power plants
- 5. Telephone lines
Select the correct answer using the code given below.
Answer (b) & explanation
Vehicle brakes, engines and power plants produce magnetite (b). Magnetite is a magnetic iron oxide. Its tiny nanoparticles come from combustion and friction. Item 1 is right: brake wear grinds off iron particles. Item 2 is right: vehicle engines release them in exhaust. Item 4 is right: burning coal and other fuels in power plants produces them. Items 3 and 5 are wrong: microwave ovens and telephone lines give off no such particles.
Notice the 2016 study (Maher and others) that found magnetite particles in human brain tissue and linked them to air pollution, raising concern about Alzheimer's disease. Such particles fall within PM2.5, which the National Clean Air Programme (2019) aims to reduce.
Answer as per the official UPSC answer key.
The ‘Common Carbon Metric’, supported by UNEP, has been developed for
Answer (a) & explanation
It assesses the carbon footprint of building operations (a). The Common Carbon Metric was developed by UNEP's Sustainable Buildings and Climate Initiative (UNEP-SBCI). It gives one standard way to measure the energy use and greenhouse gas emissions of buildings in operation, so that buildings anywhere in the world can be compared and reported on the same basis. Option (b) is wrong: it is not for farm carbon trading. Option (c) is wrong: national footprints are reported through UNFCCC inventories. Option (d) is wrong: it does not measure global fossil fuel use.
Notice that buildings account for nearly 40% of global energy-related emissions. India's tools include the Energy Conservation Building Code (ECBC) and the GRIHA green rating system.
Answer as per the official UPSC answer key.
Bisphenol A (BPA), a cause of concern, is a structural/key component in the manufacture of which of the following kinds of plastics?
Answer (b) & explanation
BPA is a key component of polycarbonate (b). Bisphenol A is the building block of hard, clear polycarbonate plastic, used in water bottles and food containers, and of epoxy resins that line food cans. It can leach into food and drinks, especially when heated, and acts like the hormone oestrogen, making it an endocrine disruptor. Low-density polyethylene (a) is used in bags. PET (c) is used in most soft-drink bottles. PVC (d) is used in pipes. None of them is built from BPA.
Notice that India, through the BIS, banned BPA in baby feeding bottles in 2015. Phthalates are another group of plastic chemicals that disrupt hormones.
Answer as per the official UPSC answer key.
‘Triclosan’, considered harmful when exposed to high levels for a long time, is most likely present in which of the following?
Answer (d) & explanation
Triclosan is most likely in toiletries (d). Triclosan is an antibacterial and antifungal agent added to soaps, toothpastes, deodorants, hand washes and some cosmetics. Long exposure at high levels is linked to hormone disruption, especially of thyroid hormones, and to germs becoming resistant to antibiotics. It also builds up in rivers and harms aquatic life. It is not used in food preservatives (a), fruit-ripening agents (b) such as calcium carbide or ethylene, or in reused plastic containers (c).
Notice that the US FDA banned triclosan in consumer antiseptic hand washes in 2016. Notice related concerns: antimicrobial resistance (AMR), which India tackles under its National Action Plan on AMR.
Answer as per the official UPSC answer key.
‘R2 Code of Practices’ constitutes a tool available for promoting the adoption of
Answer (a) & explanation
R2 promotes responsible electronics recycling (a). R2, short for "Responsible Recycling", is a certification standard for firms that repair, refurbish and recycle electronics. It covers the safe handling of e-waste, data security when old devices are wiped, worker health and safety, and tracking of materials through the recycling chain. Option (b) is a trap: the "R" stands for recycling, not Ramsar. Option (c) is wrong: it does not deal with crops on degraded land. Option (d) is wrong: it is not an EIA tool.
Notice India's E-Waste (Management) Rules, 2022, based on Extended Producer Responsibility (EPR). India is among the world's top three e-waste producers, after China and the US.
Answer as per the official UPSC answer key.
Which of the following are the reasons/factors for exposure to benzene pollution ?
- 1. Automobile exhaust
- 2. Tobacco smoke
- 3. Wood burning
- 4. Using varnished wooden furniture
- 5. Using products made of polyurethane
Select the correct answer using the code given below :
Answer (a) & explanation
Factors 1, 2 and 3 are correct in UPSC's key (a). Benzene is released when carbon-rich material burns incompletely. Major sources are vehicle exhaust (1), as benzene is in petrol and is formed during burning; tobacco smoke (2), the main source for smokers; and wood burning (3), including stoves and forest fires. Benzene is a known cause of leukaemia and other blood cancers. UPSC's key leaves out varnished furniture (4) and polyurethane products (5), which give off other volatile organic compounds such as formaldehyde.
Notice India's limits: BS-VI fuel (from 2020) limits benzene in petrol to 1%, and the National Ambient Air Quality Standards set a yearly limit of 5 µg/m³. Petrol pumps use vapour recovery systems.
Answer as per the official UPSC answer key.
Steel slag can be the material for which of the following ?
- 1. Construction of base road
- 2. Improvement of agricultural soil
- 3. Production of cement
Select the correct answer using the code given below :
Answer (d) & explanation
Steel slag can be used for all three (d). Steel slag is the stony waste left over when lime is used to remove impurities from molten iron in steel-making. Use 1 is right: crushed slag is hard and strong, so it is used in road base and sub-base layers; India's first steel slag road was built in Surat (2022). Use 2 is right: slag is rich in lime (calcium) and some silicates, so it can correct acidic soils. Use 3 is right: granulated blast furnace slag is ground into Portland Slag Cement, cutting the need for clinker.
Notice the idea of a circular economy: turning industrial waste into resources. Fly ash from power plants is reused the same way, in bricks and cement.
Answer as per the official UPSC answer key.
In rural road construction, the use of which of the following is preferred for ensuring environmental sustainability or to reduce carbon footprint ?
- 1. Copper slag
- 2. Cold mix asphalt technology
- 3. Geotextiles
- 4. Hot mix asphalt technology
- 5. Portland cement
Select the correct answer using the code given below :
Answer (a) & explanation
Copper slag, cold mix asphalt and geotextiles are preferred (a). Item 1 is right: copper slag reuses an industrial waste in place of natural sand and aggregate. Item 2 is right: cold mix asphalt is laid without heating, saving fuel and emissions, and it works in rain and cold hill areas. Item 3 is right: geotextiles, such as jute or coir mats, strengthen the road and control erosion with less material. Item 4 is wrong: hot mix asphalt needs heating to about 150 °C, which burns fuel. Item 5 is wrong: making Portland cement releases a lot of CO₂.
Notice PMGSY (Pradhan Mantri Gram Sadak Yojana, 2000), which promotes green technologies in rural roads, including waste plastic, fly ash and these materials.
Answer as per the official UPSC answer key.
Consider the following statements :
- 1. Coal ash contains arsenic, lead and mercury.
- 2. Coal-fired power plants release sulphur dioxide and oxides of nitrogen into the environment.
- 3. High ash content is observed in Indian coal.
Which of the statements given above is/are correct ?
Answer (d) & explanation
All three statements are correct (d). Statement 1 is right: coal fly ash carries toxic metals such as arsenic, lead and mercury, which can leak into water and soil from ash ponds. Statement 2 is right: burning coal releases sulphur dioxide (SO₂) and oxides of nitrogen (NOₓ), which cause acid rain and smog, along with particulate matter. Statement 3 is right: most Indian coal is low grade, with 30–45% ash, far more than imported coal, so plants produce huge amounts of ash.
Notice the response: Flue Gas Desulphurisation (FGD) units to cut SO₂, and rules for 100% fly ash use in bricks, cement and roads. Indian coal is low in sulphur, which is one benefit.
Answer as per the official UPSC answer key.
Consider the following statements :
- 1. 36% of India’s districts are classified as “overexploited” or “critical” by the Central Ground Water Authority (CGWA).
- 2. CGWA was formed under the Environment (Protection) Act.
- 3. India has the largest area under groundwater irrigation in the world.
Which of the statements given above is/are correct ?
Answer (b) & explanation
Statements 2 and 3 are correct (b). Statement 1 is wrong per the key: assessments by the Central Ground Water Board classify blocks, not whole districts, as over-exploited or critical, and the figures did not match 36% of districts by the CGWA. Statement 2 is right: the Central Ground Water Authority was set up in 1997 under Section 3(3) of the Environment (Protection) Act, 1986, to regulate groundwater use. Statement 3 is right: India uses more groundwater than any other country and has the largest area irrigated by it.
Notice Atal Bhujal Yojana (2019), which works on community groundwater management in seven States. Punjab, Haryana and Rajasthan have the worst over-extraction.
CGWB and CGWA again. The Board assesses; the Authority regulates.
Fell for this one? Most aspirants do. The PYQ Book puts every UPSC trap side by side, so the pattern finally clicks. Try the free sample
Answer as per the official UPSC answer key.
In the context of proposals to the use of hydrogen-enriched CNG (H-CNG) as fuel for buses in public transport, consider the following statements :
- 1. The main advantage of the use of H-CNG is the elimination of carbon monoxide emissions.
- 2. H-CNG as fuel reduces carbon dioxide and hydrocarbon emissions.
- 3. Hydrogen up to one-fifth by volume can be blended with CNG as fuel for buses.
- 4. H-CNG makes the fuel less expensive than CNG.
Which of the statements given above is/are correct?
Answer (b) & explanation
Statements 2 and 3 are correct (b). H-CNG blends hydrogen into compressed natural gas. Statement 3 is right because about 18–20% hydrogen by volume, roughly one-fifth, can be used in bus engines with small changes. Statement 2 is right because burning less carbon lowers CO₂ and hydrocarbon emissions. Statement 1 is wrong because it reduces carbon monoxide, by up to about 70%, but does not eliminate it. Statement 4 is wrong because hydrogen costs more than natural gas, so H-CNG is dearer than plain CNG.
Delhi ran trials on H-CNG buses from 2020. Notice the National Green Hydrogen Mission (2023), which aims at 5 million tonnes of green hydrogen a year by 2030, with hydrogen buses in Leh and Delhi.
"elimination" is too strong; H-CNG reduces CO, not removes it.
Answer as per the official UPSC answer key.
Consider the following statements :
- 1. As per recent amendment to the Indian Forest Act, 1927, forest dwellers have the right to fell the bamboos grown on forest areas.
- 2. As per the Scheduled Tribes and Other Traditional Forest Dwellers (Recognition of Forest Rights) Act, 2006, bamboo is a minor forest produce.
- 3. The Scheduled Tribes and Other Traditional Forest Dwellers (Recognition of Forest Rights) Act, 2006 allows ownership of minor forest produce to forest dwellers.
Which of the statements given above is/are correct?
Answer (b) & explanation
Statements 2 and 3 are correct (b). Statement 1 is wrong because the 2017 amendment to the Indian Forest Act, 1927 removed bamboo grown outside forests from the definition of "tree". So it can be cut and moved without permits, helping farmers earn from it. It did not give forest dwellers a right to fell bamboo inside forests. Statement 2 is right because the Forest Rights Act, 2006 lists bamboo as minor forest produce, along with tendu leaves, honey and lac. Statement 3 is right because the Act gives forest dwellers the right of ownership, access to collect, use and sell minor forest produce.
Notice the success story: Mendha Lekha village in Gadchiroli, Maharashtra, became the first to earn from bamboo under community rights. The National Bamboo Mission was restructured in 2018.
the 2017 change was about bamboo outside forests. The question says "forest areas".
Answer as per the official UPSC answer key.
Consider the following statements :
The Environment Protection Act, 1986 empowers the Government of India to
- 1. state the requirement of public participation in the process of environmental protection, and the procedure and manner in which it is sought
- 2. lay down the standards for emission or discharge of environmental pollutants from various sources
Which of the statements given above is/are correct?
Answer (b) & explanation
Only statement 2 is correct (b). The Environment (Protection) Act, 1986, passed after the Bhopal gas tragedy, is an "umbrella" law. Section 3 gives the Centre wide powers, including setting standards for emissions and discharges of pollutants from various sources (2), restricting industries in certain areas, and handling hazardous substances. Statement 1 is wrong because the Act itself says nothing about public participation. Public hearings come from the EIA Notification (1994, 2006) issued under the Act.
The Act also lets the Centre set up authorities, such as the CAQM for Delhi's air. Notice the 2023 Jan Vishwas changes, which replaced jail terms for many EPA violations with penalties. The draft EIA 2020 was criticised for weakening public hearings.
Answer as per the official UPSC answer key.