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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As per the Solid Waste Management Rules, 2016 in India, which one of the following statements is correct?
Answer (c) & explanation
Option (c) is correct. The Solid Waste Management Rules, 2016 give detailed criteria for choosing sites for landfills and waste processing plants, such as distance from rivers, homes and airports. Option (a) is wrong because generators must sort waste into three streams: wet (biodegradable), dry and domestic hazardous. Option (b) is wrong because the Rules apply beyond urban local bodies, to census towns, special economic zones, railways, airports, ports, defence areas and places of pilgrimage. Option (d) is wrong because there is no ban on moving waste between districts.
The Rules made bulk generators responsible for processing their waste and introduced user fees. Notice the SWM Rules, 2026 (in force from April 2026), which replaced them and require four-stream segregation: wet, dry, sanitary and special-care waste.
Answer as per the official UPSC answer key.
In India, ‘extended producer responsibility’ was introduced as an important feature in which of the following?
Answer (c) & explanation
EPR was introduced as a key feature in the e-Waste Rules, 2011 (c). Extended Producer Responsibility makes a manufacturer responsible for its products even after use, by collecting and recycling them at the end of their life. India first made it a central feature in the e-Waste (Management and Handling) Rules, 2011, which came into force in 2012. The Bio-medical Waste Rules, 1998 (a) and the Recycled Plastic Rules, 1999 (b) did not centre on EPR. The Food Safety Regulations, 2011 (d) deal with food standards.
Later, EPR spread to plastic packaging (Plastic Waste Management Rules, 2016, with EPR guidelines in 2022), batteries (2022), tyres (2022) and used oil. Notice the E-Waste Rules, 2022, which set yearly recycling targets and an online EPR portal.
Answer as per the official UPSC answer key.
In the context of which one of the following are the terms ‘pyrolysis and plasma gasification’ mentioned?
Answer (d) & explanation
These are waste-to-energy technologies (d). Pyrolysis heats waste, such as plastics or biomass, to high temperatures without oxygen. Instead of burning, the material breaks down into pyrolysis oil, gas (syngas) and char. Plasma gasification uses a plasma torch, at several thousand degrees, to break waste down into syngas (mainly hydrogen and carbon monoxide), leaving a glassy, harmless slag. Both turn waste into fuel or power and reduce the load on landfills. They are not used for extracting rare earths (a) or natural gas (b), and they are not hydrogen car technology (c), though syngas can yield hydrogen.
Notice India's rules: the Solid Waste Management Rules, 2016 (being updated) promote waste-to-energy, and the SATAT scheme backs compressed biogas from waste.
Answer as per the official UPSC answer key.
Why is there a great concern about the ‘microbeads’ that are released into environment?
Answer (a) & explanation
Microbeads harm marine ecosystems (a). Microbeads are tiny plastic balls, under 5 mm and often under 1 mm, that were added to face scrubs, toothpaste and cosmetics. They are too small to be caught by sewage plants, so they flow into rivers and seas. Fish, plankton and shellfish swallow them, and they soak up toxic chemicals, which move up the food chain to humans. They are not known to cause skin cancer (b), are not absorbed by crop plants (c), and are not food adulterants (d).
Notice the rules: the USA banned them in 2015, and India's BIS declared them unsafe for cosmetics (2017). India banned single-use plastic items from July 2022, and global talks on a plastics treaty continue.
Answer as per the official UPSC answer key.
Consider the following :
- 1. Carbon monoxide
- 2. Methane
- 3. Ozone
- 4. Sulphur dioxide
Which of the above are released into atmosphere due to the burning of crop/biomass residue?
Answer (d) & explanation
All four are released (d). Burning crop residue, such as stubble in Punjab and Haryana, gives off carbon monoxide (1) from incomplete burning, methane (2), and sulphur dioxide (4), along with soot and fine particles (PM2.5). It also releases nitrogen oxides and volatile organic compounds. These react in sunlight to form ground-level ozone (3), a secondary pollutant. UPSC's key counts ozone as released, so all four are correct.
Notice the fixes: the Happy Seeder and in-situ machines, Pusa decomposer, using stubble in power plants and 2G ethanol, and penalties set by the CAQM. Stubble fires fell sharply by 2024–25, though satellites suggest some burning has shifted to evening hours.
ozone is not given off directly; it forms from the smoke. UPSC still counts it.
UPSC repeats traps like this year after year. The PYQ Book gathers every trap in one place, so you see them coming. Try the free sample
Answer as per the official UPSC answer key.
In India, the use of carbofuran, methyl parathion, phorate and triazophos is viewed with apprehension. These chemicals are used as
Answer (a) & explanation
These chemicals are agricultural pesticides (a). Carbofuran, methyl parathion, phorate and triazophos are highly toxic insecticides. Most are organophosphates and carbamates, which harm the nervous system of insects and, in large doses, of humans and animals. Carbofuran is notorious for poisoning birds, such as sarus cranes and vultures, and for being misused in fish and wildlife poisoning. They are not food preservatives (b), fruit-ripening agents (c) such as calcium carbide or ethylene, or cosmetic moisturisers (d).
Notice India's moves: the government banned 18 pesticides after the Anupam Verma Committee and later restricted more, and the Pesticide Management Bill is pending. The Yavatmal poisonings (2017) of farmers spraying cotton made the risk clear.
Answer as per the official UPSC answer key.
Consider the following statements :
- 1. Agricultural soils release nitrogen oxides into environment.
- 2. Cattle release ammonia into environment.
- 3. Poultry industry releases reactive nitrogen compounds into environment.
Which of the statements given above is/are correct?
Answer (d) & explanation
All three statements are correct (d). These are all sources of reactive nitrogen, meaning nitrogen in forms other than inert N₂ gas. Statement 1 is right because fertilised farm soils give off nitrous oxide (N₂O), a powerful greenhouse gas, and nitric oxide, as microbes act on extra urea. Statement 2 is right because cattle dung and urine release ammonia. Statement 3 is right because poultry farms release ammonia and other nitrogen compounds from droppings. The Indian Nitrogen Assessment (2017) named all three, with cereals and livestock as the main sources.
Notice the solutions: neem-coated urea (mandatory since 2015), nano urea by IFFCO, and soil health cards. India's 2019 UNEA resolution on sustainable nitrogen management was adopted.
Answer as per the official UPSC answer key.
How is the National Green Tribunal (NGT) different from the Central Pollution Control Board (CPCB) ?
- 1. The NGT has been established by an Act whereas the CPCB has been created by an executive order of the Government.
- 2. The NGT provides environmental justice and helps reduce the burden of litigation in the higher courts whereas the CPCB promotes cleanliness of streams and wells, and aims to improve the quality of air in the country.
Which of the statements given above is/are correct ?
Answer (b) & explanation
Only statement 2 is correct (b). Statement 1 is wrong because both bodies are statutory. The CPCB was set up in 1974 under the Water (Prevention and Control of Pollution) Act and was later given powers under the Air Act, 1981 and the Environment Protection Act. The NGT was set up under the NGT Act, 2010. Statement 2 is right because the NGT gives fast environmental justice, deciding cases within six months, and reduces the load on higher courts. The CPCB works to keep streams and wells clean and to improve air quality.
The NGT's principal bench is in New Delhi, with four zonal benches. Notice the principles it applies: sustainable development, the precautionary principle, and polluter pays, under Section 20 of the NGT Act.
"executive order" is the slip. The CPCB came from a law, like the NGT.
Answer as per the official UPSC answer key.
Which of the following is/are the possible consequence/s of heavy sand mining in riverbeds ?
- 1. Decreased salinity in the river
- 2. Pollution of groundwater
- 3. Lowering of the water-table
Select the correct answer using the code given below :
Answer (b) & explanation
Statements 2 and 3 are correct (b). River sand works like a sponge and a filter. It stores water and cleans it as it seeps down into aquifers. Heavy mining deepens and lowers the riverbed, so water drains away faster and the water table falls (3). Without the sand layer, polluted surface water reaches groundwater without being filtered (2). Statement 1 is wrong because mining does not reduce salinity. Near the coast, a deeper channel lets seawater push further upstream, so salinity rises.
Other harms include eroded banks, weakened bridges and lost habitat for gharials and turtles. Notice the rules: the Sustainable Sand Mining Management Guidelines (2016) and the Enforcement and Monitoring Guidelines (2020) require district surveys and replenishment studies.
"decreased salinity" reverses what actually happens near river mouths.
Answer as per the official UPSC answer key.
In the context of solving pollution problems, what is/are the advantage/advantages of bioremediation technique ?
- 1. It is a technique for cleaning up pollution by enhancing the same biodegradation process that occurs in nature.
- 2. Any contaminant with heavy metals such as cadmium and lead can be readily and completely treated by bioremediation using microorganisms.
- 3. Genetic engineering can be used to create microorganisms specifically designed for bioremediation.
Select the correct answer using the code given below :
Answer (c) & explanation
Statements 1 and 3 are correct (c). Bioremediation uses microbes, fungi or plants to clean up pollution by speeding up the natural biodegradation that happens anyway (1). Genetic engineering can create microbes designed for particular pollutants (3). Ananda Chakrabarty's oil-eating Pseudomonas was the first patented living organism (1980). Statement 2 is wrong because heavy metals like cadmium and lead cannot be broken down. Microbes and plants can only change their form or concentrate them, as in phytoremediation. So "any ... readily and completely" goes too far.
Bioremediation is used after oil spills, and India's TERI developed Oilzapper for this. Notice the related terms: in-situ (on site) and ex-situ (removed) treatment, and bioaugmentation (adding microbes).
"any", "readily" and "completely" in one line is a strong warning sign.
Answer as per the official UPSC answer key.
It is possible to produce algae based biofuels, but what is/are the likely limitation(s) of developing countries in promoting this industry ?
- 1. Production of algae based biofuels is possible in seas only and not on continents.
- 2. Setting up and engineering the algae based biofuel production requires high level of expertise/technology until the construction is completed.
- 3. Economically viable production necessitates the setting up of large scale facilities which may raise ecological and social concerns.
Select the correct answer using the code given below :
Answer (b) & explanation
Statements 2 and 3 are correct (b). Statement 1 is wrong because algae can be grown on land in open ponds, in closed photobioreactors, and even in wastewater, not only at sea. The real hurdles for developing countries are that setting up and engineering these plants needs high expertise and technology (2), and that making the fuel pay needs large facilities, which use land, water and nutrients and may raise ecological and social concerns (3).
Algae are third-generation biofuels: they grow fast, make oil, and do not compete with food crops the way first-generation sugarcane and maize ethanol do. Notice India's biofuel path: the National Policy on Biofuels (2018, amended 2022) and the E20 petrol target, which India reached in 2025.
Answer as per the official UPSC answer key.
Biological Oxygen Demand (BOD) is a standard criterion for
Answer (c) & explanation
BOD is used to test pollution in water (c). Biochemical (Biological) Oxygen Demand is the amount of dissolved oxygen that microbes use to break down the organic matter in a water sample, usually measured over 5 days at 20°C. A high BOD means heavy organic pollution, as from sewage or dairy waste, which takes oxygen away from fish. Clean river water has a BOD under about 3 mg/L, which is the bathing standard. It has nothing to do with blood (a), forests (b), or high altitudes (d).
COD (Chemical Oxygen Demand) measures all oxidisable matter and is always higher than BOD. Notice how the CPCB uses BOD to list polluted river stretches. Low dissolved oxygen with high BOD leads to eutrophication and fish deaths.
Answer as per the official UPSC answer key.
Which of the following are the key features of ‘National Ganga River Basin Authority (NGRBA)’?
- 1. River basin is the unit of planning and management.
- 2. It spearheads the river conservation efforts at the national level.
- 3. One of the Chief Ministers of the States through which the Ganga flows becomes the Chairman of NGRBA on rotation basis.
Select the correct answer using the code given below.
Answer (a) & explanation
Statements 1 and 2 are correct (a). The NGRBA, set up in 2009 under the Environment (Protection) Act, treated the river basin as the unit of planning and management (1) and led river conservation at the national level (2). Statement 3 is wrong: the Prime Minister chaired it, not a rotating Chief Minister.
In 2016 it was replaced by the National Ganga Council, also headed by the PM, with the National Mission for Clean Ganga under it, which runs Namami Gange. Notice how basin-level planning recognises that a river's health depends on its whole catchment.
Answer as per the official UPSC answer key.
In the cities of our country, which among the following atmospheric gases are normally considered in calculating the value of Air Quality Index?
- 1. Carbon dioxide
- 2. Carbon monoxide
- 3. Nitrogen dioxide
- 4. Sulfur dioxide
- 5. Methane
Select the correct answer using the code given below.
Answer (b) & explanation
Carbon monoxide, nitrogen dioxide and sulphur dioxide are counted (b). India's National Air Quality Index, launched in 2014 and run by the CPCB, uses eight pollutants: PM₁₀, PM₂.₅, NO₂ (3), SO₂ (4), CO (2), O₃, NH₃ and lead. It has six bands from "Good" to "Severe", and the worst pollutant sets the overall value. CO₂ (1) and methane (5) are greenhouse gases that warm the planet, but they are not local health pollutants in the AQI sense. So any option with 1 or 5 is wrong.
Notice the related schemes: the National Clean Air Programme (2019) targets 40% lower particulate levels in 130 cities by 2025–26, and GRAP steps up curbs in Delhi-NCR as the AQI worsens.
CO2 and methane warm the planet, but the AQI measures harm from breathing, so they are left out.
UPSC repeats traps like this year after year. The PYQ Book gathers every trap in one place, so you see them coming. Try the free sample
Answer as per the official UPSC answer key.
What can be the impact of excessive/inappropriate use of nitrogenous fertilizers in agriculture?
- 1. Proliferation of nitrogen-fixing microorganisms in soil can occur.
- 2. Increase in the acidity of soil can take place.
- 3. Leaching of nitrate to the groundwater can occur.
Select the correct answer using the code given below.
Answer (c) & explanation
Too much urea and ammonium fertiliser makes the soil acidic (2 correct), and unused nitrate washes down into groundwater (3 correct). Statement 1 is wrong: with plenty of nitrogen available, nitrogen-fixing microbes are suppressed, not boosted. The answer is (c).
High nitrate in drinking water can cause methaemoglobinaemia ("blue baby" syndrome), and runoff causes eutrophication of lakes. India's fertiliser use is skewed towards urea, partly because it is heavily subsidised. Notice how soil health cards, neem-coated urea and nano urea all aim to correct this imbalance.
Free nitrogen gives fixers no reason to work, so they decline.
Answer as per the official UPSC answer key.
With reference to ‘fly ash’ produced by the power plants using coal as fuel, which of the following statements is/are correct?
- 1. Fly ash can be used in the production of bricks for building construction.
- 2. Fly ash can be used as a replacement for some of the Portland cement contents of concrete.
- 3. Fly ash is made up of silicon dioxide and calcium oxide only, and does not contain any toxic elements.
Select the correct answer using the code given below.
Answer (a) & explanation
Statements 1 and 2 are correct (a). Fly ash is used to make bricks and blocks (1), and it replaces part of the cement in Portland Pozzolana Cement and concrete (2). Statement 3 is wrong: besides silica, alumina, iron oxide and lime, fly ash carries traces of arsenic, lead, mercury and other toxic metals.
That is why ash ponds and their breaches pollute the land and water around power plants. Rules under the Environment (Protection) Act require thermal plants to achieve 100% utilisation of fly ash. Notice how a waste becomes a resource: the idea of a circular economy.
Answer as per the official UPSC answer key.
With reference to bio-toilets used by the Indian Railways, consider the following statements :
- 1. The decomposition of human waste in the bio-toilets is initiated by a fungal inoculum.
- 2. Ammonia and water vapour are the only end products in this decomposition which are released into the atmosphere.
Select the correct answer using the code given below.
Answer (d) & explanation
Neither statement is correct (d). The bio-toilets on Indian Railways use a DRDO bio-digester with an anaerobic bacterial inoculum, not a fungal one, so statement 1 is wrong. The technology was first developed for soldiers' waste in the cold heights of Siachen. Statement 2 is wrong because the end products are mainly methane, carbon dioxide and water, not just ammonia and water vapour.
Railways fitted bio-toilets in all coaches to end open discharge of waste onto tracks, improving hygiene and reducing rail corrosion. Notice how defence research found a civilian use supporting Swachh Bharat.
Answer as per the official UPSC answer key.
Brominated flame retardants are used in many household products like mattresses and upholstery. Why is there some concern about their use?
- 1. They are highly resistant to degradation in the environment.
- 2. They are able to accumulate in humans and animals.
Select the correct answer using the code given below.
Answer (c) & explanation
Both concerns are valid (c). Brominated flame retardants such as PBDEs are persistent: they resist breaking down in the environment (1 correct). Being fat-soluble, they bioaccumulate in humans and animals and build up along food chains (2 correct). They have been linked to hormone disruption and effects on brain development.
Several PBDEs are listed under the Stockholm Convention on Persistent Organic Pollutants (2001), which aims to eliminate or restrict such chemicals. Notice how "persistent, bioaccumulative, toxic" is the common pattern behind DDT, PCBs and these flame retardants.
Answer as per the official UPSC answer key.
Which of the following are some important pollutants released by steel industry in India?
- 1. Oxides of sulphur
- 2. Oxides of nitrogen
- 3. Carbon monoxide
- 4. Carbon dioxide
Select the correct answer using the code given below.
Answer (d) & explanation
All four are released (d). Coke ovens and blast furnaces burn coal at high heat. Sulphur in the coal gives sulphur oxides; high temperatures produce nitrogen oxides; incomplete burning in the blast furnace yields carbon monoxide; and the whole process emits large amounts of carbon dioxide. Options that leave any of these out are incomplete.
Steel is one of India's largest industrial emitters. Cleaner routes include green hydrogen-based direct reduction, scrap-based electric arc furnaces and the Green Steel taxonomy released in 2024. Notice how industry, chemistry and climate policy meet in this one sector.
Answer as per the official UPSC answer key.
Consider the following statements :
- 1. Animal Welfare Board of India is established under the Environment (Protection) Act, 1986.
- 2. National Tiger Conservation Authority is a statutory body.
- 3. National Ganga River Basin Authority is chaired by the Prime Minister.
Which of the statements given above is/are correct?
Answer (b) & explanation
Statements 2 and 3 are correct (b). The Animal Welfare Board of India (1962) was set up under the Prevention of Cruelty to Animals Act, 1960, not the Environment Act, so statement 1 is wrong. The National Tiger Conservation Authority became a statutory body through a 2006 amendment to the Wildlife (Protection) Act. The National Ganga River Basin Authority (2009) was chaired by the Prime Minister.
In 2016 the NGRBA was replaced by the National Ganga Council, also chaired by the PM, with the National Mission for Clean Ganga under it. Notice how river and wildlife bodies often draw their power from different laws.
Answer as per the official UPSC answer key.