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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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.
Consider the following pairs :
| Terms sometimes seen in the news | Their origin
| 1. Annex-I Countries | Cartagena Protocol
| 2. Certified Emissions Reductions | Nagoya Protocol
| 3. Clean Development Mechanism | Kyoto Protocol
Which of the pairs given above is/are correctly matched?
Answer (c) & explanation
Only pair 3 is correct (c). The Clean Development Mechanism comes from the Kyoto Protocol (1997). Pair 1 is wrong: Annex-I countries, the industrialised nations, are listed under the UNFCCC (1992), not the Cartagena Protocol. Pair 2 is wrong: Certified Emission Reductions are carbon credits earned under Kyoto's CDM, not the Nagoya Protocol.
Cartagena (2000) deals with the safe movement of living modified organisms, and Nagoya (2010) with access to genetic resources and benefit-sharing; both come under the CBD. Notice how the Paris Agreement's Article 6 carbon market now takes the place of the CDM, so these old terms still matter.
Cartagena and Nagoya are both CBD protocols, so neither belongs with climate terms.
Answer as per the official UPSC answer key.
Recently, for the first time in our country, which of the following States has declared a particular butterfly as ‘State Butterfly’?
Answer (d) & explanation
Maharashtra was the first (d). In 2015, Maharashtra declared the Blue Mormon (Papilio polymnestor) its State butterfly. It is a large, velvety black-and-blue swallowtail found mainly in the Western Ghats and Sri Lanka. Arunachal Pradesh (a), Himachal Pradesh (b) and Karnataka (c) were not first. Karnataka later chose the Southern Birdwing, India's largest butterfly, and Kerala chose the Malabar Banded Peacock.
Butterflies are good bio-indicators because they react quickly to habitat and climate change. Notice the trend that followed, as Uttarakhand chose the Common Peacock and Tamil Nadu the Tamil Yeoman. Expect questions on such State symbols, which tie local identity to conservation.
Answer as per the official UPSC answer key.
‘BioCarbon Fund Initiative for Sustainable Forest Landscapes’ is managed by the
Answer (d) & explanation
The BioCarbon Fund (2004) is managed by the World Bank (d). Its Initiative for Sustainable Forest Landscapes (2013) pays for lower land-use emissions across whole landscapes, including farming and forests. The ADB (a), IMF (b) and UNEP (c) do not manage it.
The World Bank also hosts the Forest Carbon Partnership Facility, which supports REDD+, and the Prototype Carbon Fund, one of the first carbon funds. Notice how the World Bank has become a central player in carbon finance, linking forests, farming and climate goals through results-based payments.
Answer as per the official UPSC answer key.
With reference to ‘Forest Carbon Partnership Facility’, which of the following statements is/are correct?
- 1. It is a global partnership of governments, businesses, civil society and indigenous peoples.
- 2. It provides financial aid to universities, individual scientists and institutions involved in scientific forestry research to develop eco-friendly and climate adaptation technologies for sustainable forest management.
- 3. It assists the countries in their ‘REDD+ (Reducing Emissions from Deforestation and Forest Degradation+)’ efforts by providing them with financial and technical assistance.
Select the correct answer using the code given below.
Answer (c) & explanation
Statements 1 and 3 are correct (c). The Forest Carbon Partnership Facility (World Bank, 2008) brings together governments, businesses, civil society and indigenous peoples (1). Its Readiness Fund and Carbon Fund help countries prepare for REDD+ and pay them for verified emission cuts (3). Statement 2 is wrong: it does not give research grants to universities or individual scientists.
REDD+ pays developing countries to keep forests standing, also rewarding conservation and sustainable management. Notice how forests are treated as climate assets, linking this to the BioCarbon Fund in the previous question.
Answer as per the official UPSC answer key.
With reference to an organization known as ‘BirdLife International’, which of the following statements is/are correct?
- 1. It is a Global Partnership of Conservation Organizations.
- 2. The concept of ‘biodiversity hotspots’ originated from this organization.
- 3. It identifies the sites known/referred to as ‘Important Bird and Biodiversity Areas’.
Select the correct answer using the code given below.
Answer (c) & explanation
Statements 1 and 3 are correct (c). BirdLife International is a global partnership of national conservation organisations; its Indian partner is the BNHS (1). It identifies Important Bird and Biodiversity Areas (IBAs), sites vital for birds and wider biodiversity (3). Statement 2 is wrong: the biodiversity hotspot idea came from the British ecologist Norman Myers in 1988 and was later adopted by Conservation International.
BirdLife is also the Red List authority for birds within IUCN. India has four hotspots: the Himalaya, Indo-Burma, the Western Ghats–Sri Lanka and Sundaland (Nicobar). Notice how birds act as indicators of ecosystem health.
Hotspots are Myers' idea. BirdLife is known for IBAs.
Answer as per the official UPSC answer key.
Which of the following National Parks is unique in being a swamp with floating vegetation that supports a rich biodiversity?
Answer (b) & explanation
Keibul Lamjao on Loktak Lake, Manipur, is the world's only floating national park (b). It rests on phumdis, thick mats of vegetation, soil and organic matter, and is the last natural home of the sangai or brow-antlered deer, Manipur's state animal. Bhitarkanika (a) is a mangrove park in Odisha known for saltwater crocodiles. Keoladeo (c) and Sultanpur (d) are bird habitats in Rajasthan and Haryana, not floating swamps.
Loktak is a Ramsar site on the Montreux Record, threatened by the Ithai barrage and pollution. Notice how one lake links species, people and hydropower.
Answer as per the official UPSC answer key.
Which one of the following is the best description of the term ‘ecosystem’?
Answer (c) & explanation
An ecosystem is a community of organisms together with the non-living environment in which they live, such as soil, water, air and light, all working as one unit (c). Option (a) describes only a community, without the physical environment. Option (b) describes the biosphere, and option (d) describes the flora and fauna of an area.
The term was coined by A. G. Tansley in 1935. An ecosystem has producers, consumers and decomposers, with energy flowing through it and nutrients cycling within it. Notice how a pond, a forest or even an aquarium can be studied as an ecosystem.
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 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.
With reference to the International Union for Conservation of Nature and Natural Resources (IUCN) and the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), which of the following statements is/are correct?
- 1. IUCN is an organ of the United Nations and CITES is an international agreement between governments.
- 2. IUCN runs thousands of field projects around the world to better manage natural environments.
- 3. CITES is legally binding on the States that have joined it, but this Convention does not take the place of national laws.
Select the correct answer using the code given below.
Answer (b) & explanation
Statements 2 and 3 are correct (b). IUCN (1948, Gland) is a membership union of governments and NGOs, not a UN organ, though it has UN observer status, so statement 1 is wrong. IUCN runs field projects worldwide and publishes the Red List (2 correct). CITES (1973) is legally binding on its Parties, but it does not replace national laws: each country must pass its own law to apply it (3 correct).
In India, CITES is applied through the Wildlife (Protection) Act, amended in 2022 to add a schedule of CITES species. Notice how global treaties work only through domestic law.
Being a UN observer does not make IUCN a UN organ.
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.
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.
Which one of the following is the national aquatic animal of India?
Answer (c) & explanation
The Gangetic river dolphin was declared India's National Aquatic Animal in 2009 (c). It is nearly blind, finds its way and prey by echolocation, and is listed as Endangered. The saltwater crocodile (a), olive ridley turtle (b) and gharial (d) are important protected species but not the national aquatic animal.
The Vikramshila Gangetic Dolphin Sanctuary in Bihar protects it, and Project Dolphin was announced in 2020. The first nationwide count, released in 2025, found about 6,300 of them. Notice how the dolphin acts as an indicator of a healthy river, like the tiger for forests.
Answer as per the official UPSC answer key.
What is Rio+20 Conference, often mentioned in the news?
Answer (a) & explanation
Rio+20 was the UN Conference on Sustainable Development, held in Rio de Janeiro in 2012, twenty years after the 1992 Earth Summit (a). It was not a WTO ministerial (b), an IPCC meeting (c) or a CBD Conference of Parties (d).
Its outcome document, "The Future We Want", started the process that led to the Sustainable Development Goals, adopted in 2015 with 17 goals and a 2030 deadline. It also highlighted the green economy. The 1992 summit had produced the UNFCCC, the CBD and Agenda 21. Notice how this chain of summits shapes today's development agenda.
Answer as per the official UPSC answer key.
Which of the following statements regarding ‘Green Climate Fund’ is/are correct?
- 1. It is intended to assist the developing countries in adaptation and mitigation practices to counter climate change.
- 2. It is founded under the aegis of UNEP, OECD, Asian Development Bank and World Bank.
Select the correct answer using the code given below.
Answer (a) & explanation
Only statement 1 is correct (a). The Green Climate Fund was set up at Cancún (COP16, 2010) under the UNFCCC financial mechanism to help developing countries with adaptation and mitigation. Statement 2 is wrong: UNEP, the OECD, ADB and the World Bank did not found it, though the World Bank acted as its interim trustee.
Its headquarters is in Songdo, South Korea, and it aims to split funding evenly between mitigation and adaptation. Notice how climate finance remains a key North–South issue, seen in the new finance goal agreed at COP29 in Baku in 2024.
Answer as per the official UPSC answer key.
Which one of the following National Parks has a climate that varies from tropical to subtropical, temperate and arctic?
Answer (d) & explanation
Namdapha in Arunachal Pradesh rises from about 200 m to over 4,500 m at Dapha Bum. This range takes its climate from tropical rainforest through subtropical and temperate forest to snowy, near-arctic peaks (d). Khangchendzonga (a) and Nanda Devi (b) are high-altitude parks without lowland tropical forest, and Neora Valley (c) in West Bengal covers a narrower range.
Namdapha is unusual in having four big cats: tiger, leopard, clouded leopard and snow leopard, and it is home to the hoolock gibbon. Notice how altitude packs many climate zones into one park, like a journey from equator to pole.
Answer as per the official UPSC answer key.
Consider the following :
- 1. Bats
- 2. Bears
- 3. Rodents
The phenomenon of hibernation can be observed in which of the above kinds of animals?
Answer (c) & explanation
All three show it (c). Many bats hibernate in caves in winter. Bears enter a deep winter sleep, a form of hibernation in which body temperature falls only a little. Many rodents, such as ground squirrels, marmots and dormice, are true hibernators. Options (a), (b) and (d) each leave out a group that does hibernate.
Hibernation saves energy when food is scarce in cold seasons. Its summer counterpart is aestivation, seen in some snails, lungfish and frogs during heat and drought. Notice how adaptation questions often turn on temperature and food: the same logic explains migration in birds.
Answer as per the official UPSC answer key.
With reference to ‘Eco-Sensitive Zones’, which of the following statements is/are correct?
- 1. Eco-Sensitive Zones are the areas that are declared under the Wildlife (Protection) Act, 1972.
- 2. The purpose of the declaration of Eco-Sensitive Zones is to prohibit all kinds of human activities in those zones except agriculture.
Select the correct answer using the code given below.
Answer (d) & explanation
Neither statement is correct (d). Eco-Sensitive Zones are notified under the Environment (Protection) Act, 1986, not the Wildlife (Protection) Act, so statement 1 is wrong. They act as buffers around national parks and sanctuaries and regulate activities: mining and polluting industries are banned, some activities are regulated and others allowed. They do not ban everything except farming, so statement 2 is wrong.
The 2011 guidelines suggest up to 10 km around protected areas, and the Supreme Court has pressed for at least a 1 km zone. Notice how ESZs try to balance conservation with local livelihoods.
ESZs surround protected areas, but the power to notify them comes from the EPA, not the Wildlife Act.
Answer as per the official UPSC answer key.
Which of the following adds/add carbon dioxide to the carbon cycle on the planet Earth?
- 1. Volcanic action
- 2. Respiration
- 3. Photosynthesis
- 4. Decay of organic matter
Select the correct answer using the code given below.
Answer (c) & explanation
Volcanic action releases CO₂ stored in the Earth (1 correct). Respiration by plants, animals and microbes releases CO₂ (2 correct), and so does the decay of organic matter (4 correct). Photosynthesis does the opposite: it takes CO₂ out of the air and locks the carbon into plant matter, so options (a) and (d) fail.
On top of these natural flows, burning fossil fuels and clearing forests add extra carbon and drive climate change. Notice how this links biology (respiration and photosynthesis), geography (volcanoes) and environment (carbon sinks such as forests and oceans) in one cycle.
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.