Environment: previous-year questions

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.

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Items 1, 2 and 3 are correct (a). The main threats to biodiversity are habitat loss and fragmentation (2), invasive alien species such as Lantana and Prosopis in India (3), climate change (1), pollution and over-exploitation. Item 4 is wrong: vegetarianism needs less land and water than meat-heavy diets, so it reduces pressure on habitats; it is not a threat. So (b), (c) and (d) fail.

Notice the framework: E.O. Wilson's 'HIPPO' (habitat loss, invasive species, pollution, population, over-harvesting). The IPBES assessment (2019) said about 1 million species face extinction. India's National Biodiversity Strategy and Action Plan (2024) aligns with the Kunming-Montreal 30x30 target. Trap: item 4 is a lifestyle choice dressed up as a threat.

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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.

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Items 1, 3 and 4 are correct (b). The black-necked crane breeds in Ladakh and winters in Arunachal's Tawang area and Bhutan (1). Flying squirrels live in the Western Ghats, the Himalaya and the north-east (3). The snow leopard lives in the high Himalaya of Ladakh, Himachal, Uttarakhand, Sikkim and Arunachal (4). Item 2 is wrong: the Asiatic cheetah was declared extinct in India in 1952, so it was not naturally found in 2012. So (a), (c) and (d) fail.

Notice the update: African cheetahs were brought to Kuno (MP) from September 2022 under Project Cheetah, and some were moved to Gandhi Sagar in 2025. India's first snow leopard survey (2023) counted about 718. Trap: today's cheetahs are introduced, not native.

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Statement 1 only is correct (a). The National Wetland Atlas (ISRO's Space Applications Centre, 2011) found that Gujarat has the largest wetland area of any state, about a fifth of India's total, thanks to the Rann of Kutch, the Gulf of Khambhat and other coastal flats (1). Statement 2 is wrong: for India as a whole, inland wetlands (about 69%) are larger than coastal wetlands (about 27%). So (b), (c) and (d) fail.

Notice the Ramsar count: India has about 90+ Ramsar sites, the most in Asia, with Tamil Nadu having the most sites; the largest single site is the Sundarbans. The Wetlands (Conservation and Management) Rules, 2017 govern them, and Amrit Dharohar (2023) promotes them. Trap: Gujarat's coastal wetlands are huge, but nationally inland wetlands lead.

Answer as per the official UPSC answer key.

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Zero tillage only is correct per UPSC's key (b), though the key is arguable. Zero tillage leaves the soil undisturbed and keeps crop residue on top, so soil organic carbon builds up instead of being oxidised to CO₂ (3). Contour bunding mainly checks soil erosion on slopes (1); by keeping topsoil and moisture in place it can help retain carbon indirectly, so some argue for (c). Relay cropping, sowing a second crop before the first is harvested, mainly uses the season fully (2). UPSC chose the practice whose direct aim is carbon storage.

Notice the related tools: Happy Seeder machines allow sowing into rice stubble in Punjab, cutting stubble burning. Cover crops, agroforestry and biochar also store soil carbon. The '4 per 1000' initiative (COP21) promotes soil carbon. Trap: erosion control is not the same as sequestration.

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Statements 1, 2 and 3 are correct per UPSC's key (a), but item 4 is arguable. The sea absorbs CO₂ and forms carbonic acid, lowering pH and the carbonate that organisms need to build calcium carbonate shells and skeletons. This harms calcareous phytoplankton such as coccolithophores (1), coral reefs (2), and animals such as oysters and sea urchins with planktonic larval stages (3). Item 4: some plankton release dimethyl sulphide, which seeds clouds, so acidification may indirectly affect clouds; UPSC treated this as not established.

Notice the numbers: surface ocean pH has fallen from about 8.2 to 8.1 since industrialisation, about a 30% rise in acidity. A 2025 study said ocean acidification has crossed its planetary boundary. Trap: 'acid' does not mean the sea is actually acidic; it stays alkaline.

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Statements 1 and 2 are correct (a). Phytoplankton are the ocean's microscopic plants. Through photosynthesis they absorb CO₂ and, when they die and sink, carry carbon to the deep sea: the biological pump, which makes the ocean a carbon sink (1). They form the base of marine food chains, feeding zooplankton, fish and whales (2). Statement 3 is wrong: seawater density depends on temperature and salinity, not on plankton. So (b), (c) and (d) fail.

Notice the scale: phytoplankton produce about half of the world's oxygen. Ocean warming and acidification threaten them, and blooms can turn harmful. Satellites track them through ocean colour, as India's Oceansat does to forecast fishing zones. Trap: losing plankton would not change water density.

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The infrared part is correct (d). Carbon dioxide lets visible sunlight pass, but it absorbs infrared (heat) radiation, mainly the long-wave radiation given off by the warmed Earth, and some of the infrared in sunlight. It then re-radiates this heat in all directions, including back to the surface: the greenhouse effect. (a) is wrong: CO₂ does not absorb water vapour. (b) is wrong: ultraviolet is absorbed mainly by ozone in the stratosphere. (c) is wrong: CO₂ is transparent to most visible light.

Notice the numbers: CO₂ has risen from about 280 ppm before industrialisation to over 420 ppm, and 2024 was the first calendar year above 1.5°C of warming. Water vapour is the largest greenhouse gas, and methane is far stronger per molecule. Trap: the question says 'solar radiation', but the key effect is on the Earth's own infrared.

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A drug used for treating cattle is correct (b). Vultures feeding on carcasses of cattle treated with the painkiller diclofenac died of kidney failure and visceral gout. More than 95% of India's Gyps vultures (white-rumped, long-billed, slender-billed) were lost between the 1990s and 2000s. (a), (c) and (d) are wrong: invasive species, food shortage and a disease were not the main cause; carcasses were plentiful.

Notice the response: veterinary diclofenac was banned in 2006, and in 2023 India also banned aceclofenac and ketoprofen for animals. The Vulture Action Plan 2020–25 set up breeding centres, such as Pinjore in Haryana, and safe zones. Without vultures, feral dogs and rabies rose. International Vulture Awareness Day is the first Saturday of September. Trap: the cause was human-made, not natural.

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Bandipur, Manas and Sundarbans are correct (b). Bandipur (Karnataka), Manas (Assam) and Sundarbans (West Bengal) were among the first nine Project Tiger reserves of 1973–74. Item 2 is wrong: Bhitarkanika (Odisha) is a mangrove national park and Ramsar site famous for saltwater crocodiles, not a tiger reserve. So (a), (c) and (d) fail.

Notice the current count: India has 58 tiger reserves (the latest being Madhav, MP, in March 2025). The 2022 estimate counted at least 3,167 tigers (about 3,682 by full analysis), about 75% of the world's wild tigers. Odisha's tiger reserves are Similipal and Satkosia. Trap: Bhitarkanika sounds like a big Odisha reserve but is for crocodiles.

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National Parks is correct (b). National Parks have the strictest protection under the Wildlife (Protection) Act, 1972: no grazing and no collection of forest produce or biomass; rights are settled and extinguished. (d) is wrong: sanctuaries may allow some regulated rights of local people. (a) is wrong: biosphere reserves have buffer and transition zones where people live and use resources. (c) is wrong: Ramsar wetlands follow the 'wise use' principle and allow sustainable use.

Notice the numbers: India has about 106 national parks and over 570 sanctuaries. The Forest Rights Act, 2006 also recognises community rights, which creates tension in critical wildlife habitats. Conservation and community reserves (2002 amendment) are other categories. Trap: only the core legal category bans all collection.

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All three are correct (d). Bees are the best-known pollinators of crops and wild plants. Birds, such as sunbirds in India and hummingbirds in the Americas, pollinate many red and tubular flowers (ornithophily). Bats, especially fruit and nectar bats, pollinate night-blooming plants such as banana, durian, mahua and agave (chiropterophily). So options (a), (b) and (c) leave out real pollinators.

Notice the stakes: about 75% of leading food crops benefit from animal pollination. Pollinator decline from neonicotinoid pesticides, habitat loss and climate change worries scientists; the EU restricted neonicotinoids in 2018. India's National Beekeeping and Honey Mission (2020) promotes the 'Sweet Revolution'. Trap: bats are often seen only as pests.

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The answer is (b). The Himalaya is rich in species because it is a meeting point of different biogeographic realms: the Palaearctic (Eurasian) to the north, the Indo-Malayan (Oriental) to the east and south, and elements from the Ethiopian (African) realm in the west. Its great altitudinal range, from tropical foothills to alpine zones, packs many habitats into a short distance. Option (a) is wrong because rainfall varies widely, from wet east to dry west and the cold desert of Ladakh. Option (c) is wrong because invasive species, such as Lantana, have spread there. Option (d) is wrong because human pressure is heavy.

Notice the classification: India's Biogeographic Zones (Rodgers and Panwar) number 10, and the Himalaya and Trans-Himalaya are two of them. The Himalaya is part of a global biodiversity hotspot. The eastern Himalaya is richer than the western. Trap: rainfall is not the main reason.

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All four Acts are relevant (c). The Import and Export (Control) Act, 1947 (now replaced by the Foreign Trade Act, 1992) and the Customs Act, 1962 regulate the movement of wildlife, plants and biological material across borders, helping enforce CITES and stop smuggling (1, 3). The Mines and Minerals (Development and Regulation) Act, 1957 governs mining, which affects forests and habitats and requires environmental clearances (2). The Indian Forest Act, 1927 protects forests through reserved and protected forests (4). So options (a), (b) and (d) fail.

Notice the core law: the Biological Diversity Act, 2002, amended in 2023, set up the National Biodiversity Authority (Chennai), State Biodiversity Boards and local Biodiversity Management Committees. Other key laws are the Wildlife (Protection) Act, 1972 (amended 2022) and the Forest (Conservation) Act, 1980, renamed Van (Sanrakshan Evam Samvardhan) Adhiniyam in 2023. Trap: trade laws also protect biodiversity.

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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.

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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.

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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.

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Respiration, decay and volcanic action add CO₂, so the answer is (c). Respiration by plants, animals and microbes releases carbon dioxide (2). Decay of organic matter by decomposers releases it too (3). Volcanic eruptions vent CO₂ from deep inside the Earth (4). Statement 1 is wrong: photosynthesis does the reverse; it removes CO₂ from the air and stores the carbon in plants. So (a), (b) and (d) fail.

Notice the wider cycle: the oceans are the biggest carbon sink, forests and soils store a large share, and burning fossil fuels is the main human addition, pushing atmospheric CO₂ above 420 ppm today. Trap: photosynthesis is part of the carbon cycle but it is a sink, not a source.

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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.

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