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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If you walk through countryside, you are likely to see some birds stalking alongside the cattle to seize the insects disturbed by their movement through grasses. Which of the following is/are such bird/birds?
- 1. Painted Stork
- 2. Common Myna
- 3. Black-necked Crane
Select the correct answer using the code given below.
Answer (b) & explanation
The common myna walks beside grazing cattle and snaps up insects stirred up from the grass (b), as does the cattle egret. The painted stork is a wading bird that feeds on fish in shallow water, not beside cattle. The black-necked crane lives in high-altitude wetlands of Ladakh and Tibet and winters in places like Arunachal Pradesh and Bhutan, far from lowland fields.
This feeding pattern is a kind of commensalism: the bird benefits and the cattle are largely unaffected. Notice how everyday rural sights become ecology questions on species interactions.
Answer as per the official UPSC answer key.
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.
Lichens, which are capable of initiating ecological succession even on a bare rock, are actually a symbiotic association of
Answer (b) & explanation
A lichen is a symbiotic association of a fungus with an alga or a cyanobacterium (b). The fungus provides shelter and holds water; the alga makes food by photosynthesis. Options with bacteria and fungi (c), algae and bacteria (a), or fungi and mosses (d) do not describe a lichen, though some lichens do include cyanobacteria.
Lichens are the pioneers of primary succession on bare rock: their acids slowly weather the rock into the first thin soil, preparing the way for mosses and then larger plants. They are also sensitive to sulphur dioxide, which makes them useful indicators of air pollution.
Answer as per the official UPSC answer key.
If a wetland of international importance is brought under the ‘Montreux Record’, what does it imply?
Answer (a) & explanation
The Montreux Record (1990) is a register of Ramsar sites whose ecological character has changed, is changing or is likely to change because of human interference (a). Listed sites get priority conservation attention. Option (b) invents a 5-km legal ban; Ramsar sets no such rule. Option (c) describes a cultural angle that is not the purpose of the Record. Option (d) confuses Ramsar with UNESCO's World Heritage list.
In India, Keoladeo (Rajasthan) and Loktak (Manipur) are on the Record. Chilika was removed in 2002 after it recovered: a hopeful reminder that damaged wetlands can be healed.
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.
With reference to Bombay Natural History Society (BNHS), consider the following statements :
- 1. It is an autonomous organization under the Ministry of Environment and Forests.
- 2. It strives to conserve nature through action-based research, education and public awareness.
- 3. It organizes and conducts nature trails and camps for the general public.
Which of the statements given above is/are correct?
Answer (c) & explanation
The BNHS (founded in 1883 in Mumbai) is a non-government society, not an autonomous body under the environment ministry, so statement 1 is wrong. It does action-based research, education and public awareness (2 correct), and it runs nature trails and camps for the public (3 correct).
Its best-known figure is Salim Ali, the "Birdman of India", and it is BirdLife International's partner in India. BNHS research has shaped work on vultures, bustards and Important Bird Areas. Notice how UPSC often tests whether an organisation is governmental or not: a quick check that removes many wrong options.
Getting government grants does not make the BNHS a government body.
Answer as per the official UPSC answer key.
Every year, a monthlong ecologically important campaign/festival is held during which certain communities/tribes plant saplings of fruit-bearing trees. Which of the following are such communities/tribes?
Answer (b) & explanation
The Gond and Korku tribes of Madhya Pradesh, mainly in Betul and Harda districts, hold a month-long tree-planting festival in the monsoon, planting saplings of fruit trees such as mango and jamun (b). The other pairs are real tribes but not linked to this festival: Bhutia and Lepcha of Sikkim, Irula and Toda of the Nilgiris, and Sahariya and Agariya of central India.
It is a living example of community conservation, where faith and custom protect nature. Notice how this echoes sacred groves, the Bishnois of Rajasthan and the Chipko movement: forests often survive best where people see themselves as their keepers.
Answer as per the official UPSC answer key.
With reference to ‘Global Environment Facility’, which of the following statements is/are correct?
Answer (a) & explanation
The GEF (1991) is the financial mechanism for the CBD and the UNFCCC (a), and also for the UNCCD, the Stockholm Convention on POPs and the Minamata Convention on mercury. Option (b) is wrong because the GEF funds projects but does not carry out scientific research itself, so (d) also fails. Option (c) is wrong: the GEF is not an OECD agency. The World Bank acts as its trustee, and UNDP, UNEP and others implement its projects.
Notice how the GEF links the three Rio conventions of 1992: biodiversity, climate and desertification share one funding window.
Answer as per the official UPSC answer key.
Consider the following pairs :
| Wetlands | Confluence of rivers
| 1. Harike Wetlands | Confluence of Beas and Satluj/Sutlej
| 2. Keoladeo Ghana National Park | Confluence of Banas and Chambal
| 3. Kolleru Lake | Confluence of Musi and Krishna
Which of the above pairs is/are correctly matched?
Answer (a) & explanation
Only pair 1 is correct (a). Harike wetland in Punjab formed behind a barrage at the confluence of the Beas and Sutlej. Keoladeo in Bharatpur lies at the confluence of the Gambhir and Banganga rivers, not the Banas and Chambal. Kolleru Lake in Andhra Pradesh lies between the Godavari and Krishna deltas, not at a Musi–Krishna meeting point.
All three are Ramsar sites. Keoladeo is also a UNESCO World Heritage Site and was once the winter home of the Siberian crane. Notice how many Indian wetlands owe their existence to rivers and even to human-made barrages.
Answer as per the official UPSC answer key.
Consider the following pairs :
- 1. Dampa Tiger Reserve : Mizoram
- 2. Gumti Wildlife Sanctuary : Sikkim
- 3. Saramati Peak : Nagaland
Which of the above pairs is/are correctly matched?
Answer (c) & explanation
Dampa Tiger Reserve is in Mizoram, on the Bangladesh border (1 correct). Saramati (about 3,840 m) is the highest peak of Nagaland, on the Myanmar border (3 correct). Pair 2 is wrong: Gumti Wildlife Sanctuary is in Tripura, not Sikkim, so options (b) and (d) fall away.
Gumti is named after the Gumti river, whose dam created the Dumbur lake. Sikkim's protected areas include Khangchendzonga National Park, India's first "mixed" World Heritage Site. Notice how UPSC mixes north-eastern states in pairs questions: placing each site on a mental map of the region is the surest defence.
Answer as per the official UPSC answer key.
The most important strategy for the conservation of biodiversity together with traditional human life is the establishment of
Answer (a) & explanation
Biosphere reserves, under UNESCO's Man and the Biosphere programme (1971), are designed to conserve biodiversity together with human life (a). They have a strictly protected core, a buffer and a transition zone where people keep living and farming. Botanical gardens (b) are ex situ conservation. National parks (c) allow almost no human activity, and wildlife sanctuaries (d) allow some but are not built around community life.
India has 18 biosphere reserves, of which 13 are on UNESCO's world network, the first being the Nilgiri and the latest the Cold Desert (2025). Notice how this model treats people as part of the solution.
Answer as per the official UPSC answer key.
With reference to a conservation organization called ‘Wetlands International’, which of the following statements is/are correct?
- 1. It is an intergovernmental organization formed by the countries which are signatories to Ramsar Convention.
- 2. It works at the field level to develop and mobilize knowledge, and use the practical experience to advocate for better policies.
Select the correct answer using the code given below.
Answer (b) & explanation
Wetlands International is a global non-profit NGO, headquartered in the Netherlands. It is not an intergovernmental body formed by the Ramsar parties, so statement 1 is wrong. It does work at the field level, builds knowledge and uses that experience to advocate for better policies (2 correct).
It is one of the official International Organisation Partners of the Ramsar Convention, along with bodies like BirdLife, IUCN and WWF. It also has a South Asia office in New Delhi. Notice how "partner of a convention" and "created by a convention" are two different things, a distinction UPSC likes to test.
Answer as per the official UPSC answer key.
The scientific view is that the increase in global temperature should not exceed 2°C above pre-industrial level. If the global temperature increases beyond 3°C above the pre-industrial level, what can be its possible impact/impacts on the world?
- 1. Terrestrial biosphere tends toward a net carbon source.
- 2. Widespread coral mortality will occur.
- 3. All the global wetlands will permanently disappear.
- 4. Cultivation of cereals will not be possible anywhere in the world.
Select the correct answer using the code given below.
Answer (b) & explanation
The IPCC's Fourth Assessment (2007) warned that above about 3°C of warming, the terrestrial biosphere would tend to become a net carbon source, releasing more carbon than it absorbs (1 correct), and that widespread coral mortality would occur (2 correct). Statements 3 and 4 use extreme words: "all" wetlands vanishing permanently and cereals failing "anywhere" go far beyond the science, so the answer is (b).
The Paris Agreement (2015) aims to keep warming well below 2°C and pursue 1.5°C. Notice how words like "all", "only" and "anywhere" are often UPSC's signal of a wrong statement.
"All ... permanently" and "anywhere in the world": absolute words like these give the wrong statements away.
Answer as per the official UPSC answer key.
Other than poaching, what are the possible reasons for the decline in the population of Ganges River Dolphins?
- 1. Construction of dams and barrages on rivers
- 2. Increase in the population of crocodiles in rivers
- 3. Getting trapped in fishing nets accidentally
- 4. Use of synthetic fertilizers and other agricultural chemicals in crop-fields in the vicinity of rivers.
Select the correct answer using the code given below.
Answer (c) & explanation
Dams and barrages fragment dolphin populations and reduce flow (1 correct). Dolphins drown as bycatch in fishing nets (3 correct), and farm chemicals washing into rivers poison their habitat (4 correct). Statement 2 is wrong: crocodile numbers are themselves low and crocodiles are not a cause of decline, so options (a), (b) and (d) fail.
The Ganges River Dolphin is India's national aquatic animal (2009) and is listed as Endangered. It is nearly blind and finds prey by echolocation. Project Dolphin (2020) and the Vikramshila Gangetic Dolphin Sanctuary in Bihar work for its protection. Notice how its health is a sign of the river's health.
Answer as per the official UPSC answer key.
Consider the following international agreements :
- 1. The International Treaty on Plant Genetic Resources for Food and Agriculture
- 2. The United Nations Convention to Combat Desertification
- 3. The World Heritage Convention
Which of the above has/have a bearing on the biodiversity?
Answer (d) & explanation
All three bear on biodiversity (d). The Plant Treaty (FAO, 2001) conserves the genetic diversity of crops and shares their benefits (1). The UNCCD (1994) protects drylands and the life they support (2). The World Heritage Convention (1972) protects natural sites such as Kaziranga, Manas and the Western Ghats (3).
These sit with the CBD, CITES, the Ramsar Convention and the Convention on Migratory Species among the biodiversity-related conventions that coordinate their work. Notice how biodiversity is protected not by one treaty but by a web of them, each with its own focus.
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 one of the following is the correct sequence of a food chain?
Answer (a) & explanation
A food chain always starts with a producer. Diatoms are phytoplankton that make food by photosynthesis. Small crustaceans such as copepods graze on them, and herrings eat the crustaceans. So the order is Diatoms–Crustaceans–Herrings (a). Options (b), (c) and (d) put a consumer before the producer or reverse the order of eating.
Diatoms have glassy silica shells and produce a large share of the oxygen made in the oceans. Notice how energy shrinks at each step (roughly the 10% rule), which is why food chains rarely have more than four or five links.
Answer as per the official UPSC answer key.
Consider the following pairs :
- 1. Nokrek Biosphere Reserve : Garo Hills
- 2. Logtak (Loktak) Lake : Barail Range
- 3. Namdapha National Park : Dafla Hills
Which of the above pairs is/are correctly matched?
Answer (a) & explanation
Pair 1 only is correct (a). Nokrek is the highest peak of the Garo Hills in Meghalaya, and the Nokrek Biosphere Reserve is known for wild citrus (Citrus indica) and red pandas (1). Pair 2 is wrong: Loktak Lake, with its floating phumdis and Keibul Lamjao, the only floating national park, home of the sangai deer, lies in the Manipur valley, not the Barail Range. Pair 3 is wrong: Namdapha is in eastern Arunachal near the Patkai range; the Dafla Hills are in western Arunachal. So (b), (c) and (d) fail.
Notice the related facts: Namdapha hosts four big cats (tiger, leopard, clouded leopard, snow leopard). Loktak is a Ramsar site on the Montreux Record. Trap: real places matched to wrong hills.
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.
In the grasslands, trees do not replace the grasses as a part of an ecological succession because of
Answer (c) & explanation
Water limits and fire is correct (c). Grasslands get too little rainfall to support a full forest, and frequent fires, together with grazing, kill tree seedlings, while grasses regrow from their underground roots. Succession therefore stops at the grassland stage, a fire- or drought-maintained climax. (a) is wrong: insects and fungi affect both trees and grasses but do not stop succession. (b) is wrong: grasslands get plenty of sunlight, and their soils are often rich, as in the prairies and steppes. (d) fails because (c) is correct.
Notice India's grasslands: the terai and Kaziranga floodplain grasslands, the shola grasslands of the Nilgiris and the Banni grasslands of Kutch. Many are wrongly classed as 'wastelands' and planted with trees. Trap: (b) misreads open, sunny grasslands.
Answer as per the official UPSC answer key.