Environment: previous-year questions
273 real UPSC Prelims questions (2011–2026) with the official answer and a clear explanation. 80 of them came in the last five papers.
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Questions per year, counted from the official papers.
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A sandy and saline area is the natural habitat of an Indian animal species. The animal has no predators in that area but its existence is threatened due to the destruction of its habitat. Which one of the following could be that animal ?
Answer (b) & explanation
Indian wild ass is correct (b). The khur lives only in the Little Rann of Kutch, Gujarat, a flat, saline and sandy desert, protected in the Wild Ass Sanctuary (1972). Adults have almost no natural predators there, but salt pans, livestock grazing and the invasive Prosopis juliflora shrub eat into its habitat. (a) is wrong: the wild buffalo lives in wet grasslands of Assam and Chhattisgarh. (c) is wrong: the wild boar is widespread and has many predators. (d) is wrong: the chinkara (Indian gazelle) lives in Thar scrub and is hunted by wolves and dogs.
Notice the trend: the 2024 census counted about 7,670 wild asses, up from a few hundred in the 1960s. Trap: 'saline' points straight to the Rann.
Answer as per the official UPSC answer key.
Two important rivers -- one with its source in Jharkhand (and known by a different name in Odisha), and another, with its source in Odisha - merge at a place only a short distance from the coast of Bay of Bengal before flowing into the sea. This is an important site of wildlife and biodiversity and a protected area. Which one of the following could be this ?
Answer (a) & explanation
The answer is (a), Bhitarkanika. The Brahmani river rises in Jharkhand as the South Koel and Sankh, which join at Vedvyas near Rourkela, and is called the Brahmani in Odisha. The Baitarani rises in the Keonjhar hills of Odisha. The two meet near the coast in the Dhamra estuary region, forming the delta where Bhitarkanika lies. Bhitarkanika is a national park and Ramsar site with India's second-largest mangrove forest, famous for saltwater crocodiles, including some of the largest recorded. Chandipur-on-sea (b) is a beach and missile-test site, Gopalpur-on-sea (c) is a southern beach, and Simlipal (d) is an inland tiger reserve in Mayurbhanj.
Notice the nearby feature: Gahirmatha beach, next to Bhitarkanika, is among the world's largest nesting sites for Olive Ridley turtles. Trap: Simlipal is a protected area in Odisha but lies far from the coast.
Answer as per the official UPSC answer key.
Biodiversity forms the basis for human existence in the following ways :
- 1. Soil formation
- 2. Prevention of soil erosion
- 3. Recycling of waste
- 4. Pollination of crops
Select the correct answer using the codes given below :
Answer (d) & explanation
All four are correct (d). Biodiversity supports human life through ecosystem services. Microbes, fungi and earthworms break down rock and litter to form soil (1). Roots and plant cover hold soil against wind and water erosion (2). Decomposers recycle wastes and return nutrients to the soil (3). Bees, butterflies, birds and bats pollinate crops (4). So options (a), (b) and (c) leave out real services.
Notice the wider frame: the Millennium Ecosystem Assessment groups services as provisioning, regulating, supporting and cultural. Soil formation and nutrient cycling are supporting services; pollination and erosion control are regulating ones. The Kunming-Montreal Global Biodiversity Framework (2022) aims to protect 30% of land and sea by 2030.
Answer as per the official UPSC answer key.
Regarding “carbon credits”, which one of the following statements is *not* correct ?
Answer (d) & explanation
Statement (d) is not correct, so it is the answer. Carbon credits came with the Kyoto Protocol (1997) (a), through mechanisms like the Clean Development Mechanism (CDM) and emissions trading. One credit equals the reduction of one tonne of CO₂ or its equivalent. Countries or entities that cut emissions below their quota earn credits (b) and can sell them, so the goal is to limit emissions (c). But their price is set by supply and demand in carbon markets, not fixed by the UNEP, which makes (d) false.
Notice the new framework: under the Paris Agreement, Article 6 sets up new carbon market rules, finalised at COP29 (Baku, 2024). India launched its own Carbon Credit Trading Scheme (CCTS) under the Energy Conservation (Amendment) Act, 2022, with emission-intensity targets for industries notified in 2025. Trap: the UN body does not fix prices; the market does.
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.
Three of the following criteria have contributed to the recognition of Western Ghats-Sri Lanka and Indo-Burma regions as hotspots of biodiversity :
- 1. Species richness
- 2. Vegetation density
- 3. Endemism
- 4. Ethno-botanical importance
- 5. Threat perception
- 6. Adaptation of flora and fauna to warm and humid conditions
Which three of the above are correct criteria in this context ?
Answer (c) & explanation
Criteria 1, 3 and 5 are correct (c). A biodiversity hotspot, a concept from Norman Myers (1988) later adopted by Conservation International, must meet two strict tests: it must have at least 1,500 endemic vascular plant species (endemism), and it must have lost at least 70% of its original habitat (threat). Such places also have high species richness. So 1, 3 and 5 are the criteria. Vegetation density (2), ethno-botanical importance (4) and adaptation to warm humid conditions (6) are not hotspot criteria, so options (a), (b) and (d) fail.
Notice the numbers: there are 36 hotspots worldwide, covering about 2.5% of land but holding over half of plant species as endemics. India has parts of four: the Himalaya, Indo-Burma, Western Ghats-Sri Lanka and Sundaland (Nicobar Islands). Trap: dense forest alone does not make a hotspot.
Answer as per the official UPSC answer key.
Which one of the following is *not* a site for *in-situ* method of conservation of flora ?
Answer (b) & explanation
Botanical garden is correct (b), since it is not in-situ. In-situ conservation protects species in their natural habitat, as in biosphere reserves (a), national parks (c) and wildlife sanctuaries (d). A botanical garden grows plants away from where they live naturally, so it is ex-situ conservation, like zoos, seed banks, gene banks and tissue culture labs. So (a), (c) and (d) are in-situ.
Notice the examples: India has 18 biosphere reserves, 13 of them in UNESCO's network, and 106 national parks. The National Bureau of Plant Genetic Resources in Delhi runs a national gene bank, and the Svalbard Global Seed Vault in Norway is the world's back-up. Trap: 'garden' sounds natural, but it is still ex-situ.
Answer as per the official UPSC answer key.
Human activities in the recent past have caused the increased concentration of carbon dioxide in the atmosphere, but a lot of it does not remain in the lower atmosphere because of
- 1. its escape into the outer stratosphere.
- 2. the photosynthesis by phytoplankton in the oceans.
- 3. the trapping of air in the polar ice caps.
Which of the statements given above is/are correct ?
Answer (b) & explanation
Only statement 2 is correct (b). The oceans absorb roughly a quarter of the CO₂ humans emit, and phytoplankton, microscopic plants in sunlit surface waters, fix large amounts of it through photosynthesis. When they die, some of that carbon sinks to the deep sea, a process called the biological pump. Statement 1 is wrong: CO₂ does not escape to the outer stratosphere in any significant amount; it is well mixed in the atmosphere. Statement 3 is wrong: air bubbles trapped in polar ice are a tiny, ancient store, useful to scientists for studying past climates, not a sink for today's CO₂. So options (a), (c) and (d) fail.
Notice the cost: absorbing CO₂ makes seawater more acidic, called ocean acidification, which harms corals and shellfish. Forests and soils are the other major carbon sinks. Atmospheric CO₂ passed about 425 ppm in 2025. Trap: ice cores are records, not sinks.
Answer as per the official UPSC answer key.
The 2004 Tsunami made people realize that mangroves can serve as a reliable safety hedge against coastal calamities. How do mangroves function as a safety hedge ?
Answer (d) & explanation
Option (d) is correct. Mangroves have dense prop and stilt roots anchored deep in coastal mud, so storms and tides rarely uproot them. This tangle of roots and trunks breaks the force of waves and traps sediment, as seen in Tamil Nadu's Pichavaram and Muthupet in 2004, where villages behind mangroves suffered far less. (a) is wrong: people do live near and work in mangroves; fishing and honey collection are common. (b) is wrong: food and medicine are real benefits, but they do not make a safety hedge. (c) is wrong: most mangroves are low trees, not tall shelters.
Notice the scale: India has about 4,990 sq km of mangroves, with the Sundarbans the largest; the MISHTI scheme (2023) plants new mangroves along the coast.
Answer as per the official UPSC answer key.
In the context of ecosystem productivity, marine upwelling zones are important as they increase the marine productivity by bringing the
- 1. decomposer microorganisms to the surface.
- 2. nutrients to the surface.
- 3. bottom-dwelling organisms to the surface.
Which of the statements given above is/are correct ?
Answer (b) & explanation
Only statement 2 is correct (b). In upwelling zones, winds push surface water away from the coast, and cold, deep water rises to replace it. This deep water is rich in nutrients such as nitrates and phosphates (2). In the sunlit surface, these nutrients cause phytoplankton blooms, which feed zooplankton and fish, making upwelling zones among the most productive fisheries. Statements 1 and 3 are wrong: upwelling does not specially bring up decomposers or bottom-dwelling organisms. So options (a), (c) and (d) fail.
Notice the famous examples: the coasts of Peru (Humboldt current, anchovy fishery), Namibia (Benguela), California and northwest Africa, and in India the Kerala coast during the monsoon, which supports oil sardine catches. During El Niño, upwelling off Peru weakens, and fish catches collapse. Upwelling zones cover about 1% of the ocean but give a large share of the world's fish. Trap: nutrients, not organisms, are lifted.
Answer as per the official UPSC answer key.
The “Red Data Books” published by the International Union for Conservation of Nature and Natural Resources (IUCN) contain lists of
- 1. Endemic plant and animal species present in the biodiversity hotspots.
- 2. Threatened plant and animal species.
- 3. Protected sites for conservation of nature and natural resources in various countries.
Select the correct answer using the codes given below :
Answer (b) & explanation
Statement 2 only is correct (b). The Red Data Book, now the IUCN Red List, records species at risk of extinction, sorted into categories: Critically Endangered, Endangered and Vulnerable (together 'threatened'), plus Near Threatened, Least Concern, Extinct in the Wild and Extinct. Statement 1 is wrong: it does not list endemic species of hotspots as such; endemics appear only if they are assessed for risk. Statement 3 is wrong: protected sites are listed in the World Database on Protected Areas, not the Red List. So (a), (c) and (d) fail.
Notice the colour code: the old books used pink pages for critically endangered species and green pages for those once endangered but now safe. Trap: hotspots and protected areas are different conservation lists.
Answer as per the official UPSC answer key.
If a tropical rain forest is removed, it does not regenerate quickly as compared to a tropical deciduous forest. This is because
Answer (a) & explanation
The answer is (a). In a tropical rain forest, most nutrients are stored in the living vegetation, not in the soil. Dead matter decomposes and is recycled very fast in the hot, wet climate, and heavy rainfall leaches nutrients out of the thin soil, leaving poor laterite. When the forest is cleared, the nutrients go with the trees, and the remaining soil is too poor to support quick regrowth. Option (b) is wrong because rain forest seeds are not generally of poor viability. Option (c) is wrong because many species grow fast. Option (d) is wrong because the soil is not fertile.
Notice why this matters: slash-and-burn cultivation (jhum in Northeast India) works only with long fallow periods, since cleared land loses fertility within a few years. Deciduous forests, with slower leaching, recover faster. Trap: lush forest does not mean rich soil.
Answer as per the official UPSC answer key.
Consider the following statements :
- 1. Biodiversity is normally greater in the lower latitudes as compared to the higher latitudes.
- 2. Along the mountain gradients, biodiversity is normally greater in the lower altitudes as compared to the higher altitudes.
Which of the statements given above is/are correct ?
Answer (c) & explanation
Both statements are correct (c). Species are richest in the tropics and fall towards the poles (1). Reasons include more warmth and sunlight, high productivity, and a long, stable history without glaciation, giving more time for species to evolve. Climbing a mountain is like moving towards the poles: it gets colder and harsher, so diversity generally falls with altitude (2). So (a), (b) and (d) fail.
Notice the examples: the Amazon holds the most species of any region, and India's Western Ghats and Eastern Himalaya are biodiversity hotspots. Some groups peak at mid-elevations in mountains, but the general rule holds. Trap: both are textbook gradients, so do not look for an exception.
Answer as per the official UPSC answer key.