UPSC Prelims 2023 Environment questions: topic-wise weightage
UPSC Prelims 2023 asked 21 environment questions in GS Paper I, spread over 5 topics. See the environment weightage for 2023 below, then attempt each question with the official answer and an explanation.
Environment 2023: questions by topic
- Ecology and ecosystems2
- Biodiversity and species9
- Protected areas and conservation1
- Climate change and international conventions2
- Pollution, environmental laws and green technology7
Counted from the 21 questions on this page, tagged by topic in the Battle IAS PYQ bank.
Seeing 21 Environment questions spread over 5 topics can feel overwhelming. That's exactly why the Battle IAS PYQ Book maps every question topic by topic, so you know what to study first. Download free sample
Ecology and ecosystems 2
Consider the following trees :
- 1. Jackfruit (*Artocarpus heterophyllus*)
- 2. Mahua (*Madhuca indica*)
- 3. Teak (*Tectona grandis*)
How many of the above are deciduous trees?
Answer (b) & explanation
Two of the three are deciduous (b). A deciduous tree sheds all its leaves in one season, usually the dry summer, to save water. Teak (Tectona grandis) does this; it is the classic tree of India's tropical moist deciduous forests and is prized for its timber. Mahua (Madhuca indica) also sheds its leaves before flowering in spring; its sweet flowers are vital to tribal food and liquor. Item 1 is wrong: jackfruit (Artocarpus heterophyllus) is an evergreen tree of the wetter tracts, such as Kerala's home gardens.
Notice that tropical deciduous forests, also called monsoon forests, are India's most widespread type. Sal, sandalwood, khair and shisham also belong to this group.
Answer as per the official UPSC answer key.
Consider the following statements :
- Statement-I : The soil in tropical rain forests is rich in nutrients.
- Statement-II : The high temperature and moisture of tropical rain forests cause dead organic matter in the soil to decompose quickly.
Which one of the following is correct in respect of the above statements?
Answer (d) & explanation
Statement I is wrong but Statement II is correct (d). Statement II is right: the high heat and moisture of tropical rainforests make dead leaves and organic matter decompose very fast. Statement I is wrong: the nutrients released are taken up at once by the dense plant cover, and heavy rain washes, or leaches, the rest away. Most nutrients sit in the living plants, not the soil. So rainforest soil is poor, often red laterite rich in iron and aluminium.
Notice why clearing rainforest for farming fails: once trees are cut, the thin soil is exhausted in a few years. This explains shifting cultivation (jhum) in such areas. In contrast, cold temperate forests decompose slowly and build thick, fertile soils.
lush forest suggests rich soil. In rainforests the richness is in the plants, not the soil.
Answer as per the official UPSC answer key.
Biodiversity and species 9
Consider the following statements :
- Statement-I : Marsupials are not naturally found in India.
- Statement-II : Marsupials can thrive only in montane grasslands with no predators.
Which one of the following is correct in respect of the above statements?
Answer (c) & explanation
Statement I is correct but Statement II is wrong (c). Statement I is right: marsupials, pouched mammals such as kangaroos, live naturally only in Australia, New Guinea and the Americas, so none are native to India. Statement II is wrong: marsupials live in deserts, forests, wetlands and grasslands, often with predators; the opossum thrives in American towns. Their absence from India is a matter of history: Australia broke away from Gondwana early, and its marsupials evolved in isolation, while placental mammals came to dominate elsewhere.
Notice the term endemism: species found in only one region because of past isolation. India's own endemics, such as the lion-tailed macaque, are concentrated in the Western Ghats, a biodiversity hotspot.
Answer as per the official UPSC answer key.
‘Invasive Species Specialist Group’ (that develops Global Invasive Species Database) belongs to which one of the following organizations?
Answer (a) & explanation
The ISSG belongs to the IUCN (a). The Invasive Species Specialist Group is one of the specialist groups of the IUCN Species Survival Commission, the same body behind the Red List. It runs the Global Invasive Species Database, which lists alien species that harm native life. Option (b) is wrong: UNEP runs global environment programmes but not this group. Option (c) is wrong: the World Commission on Environment and Development (Brundtland Commission) gave the 1987 report on sustainable development. Option (d) is wrong: WWF is a separate conservation NGO.
Notice India's major invasive species: Lantana, Parthenium (congress grass), water hyacinth and Prosopis juliflora. The Kunming-Montreal framework (2022) aims to cut the arrival of invasive species by half by 2030.
Answer as per the official UPSC answer key.
Consider the following fauna :
- 1. Lion-tailed Macaque
- 2. Malabar Civet
- 3. Sambar Deer
How many of the above are generally nocturnal or most active after sunset?
Answer (a) & explanation
Only one of them is nocturnal (a). The Malabar civet, a critically endangered and possibly extinct animal of the Western Ghats, is active at night, like most civets. Item 1 is wrong: the lion-tailed macaque, also of the Western Ghats, is active by day, like most monkeys. Item 3 is treated as wrong: UPSC's key regards the sambar as feeding mainly around dawn and dusk rather than through the night, though it does turn nocturnal where hunted.
Notice the terms: nocturnal (night), diurnal (day) and crepuscular (dawn and dusk). Animals active at night often have big eyes, a sharp sense of smell or good hearing. The lion-tailed macaque is endangered, found only in rainforest canopies of Kerala, Karnataka and Tamil Nadu.
Answer as per the official UPSC answer key.
Which of the following organisms perform waggle dance for others of their kin to indicate the direction and the distance to a source of their food?
Answer (c) & explanation
Honeybees perform the waggle dance (c). A forager honeybee that finds food returns to the hive and does a figure-of-eight waggle dance on the comb. The angle of the waggle run, measured from straight up, shows the direction of the food relative to the Sun. The length of the run shows the distance. Other bees follow the dance and fly to the spot. Butterflies (a), dragonflies (b) and wasps (d) do not communicate this way.
Notice that Karl von Frisch decoded the dance and won the Nobel Prize in 1973. Bees matter far beyond honey: they pollinate many crops. India's National Beekeeping and Honey Mission pushes the Sweet Revolution.
Answer as per the official UPSC answer key.
Consider the following statements :
- 1. Some mushrooms have medicinal properties.
- 2. Some mushrooms have psycho-active properties.
- 3. Some mushrooms have insecticidal properties.
- 4. Some mushrooms have bioluminescent properties.
How many of the above statements are correct?
Answer (d) & explanation
All four statements are correct (d). Mushrooms are the fruiting bodies of fungi, and they are very varied. Statement 1 is right: reishi, shiitake and cordyceps are used in traditional and modern medicine. Statement 2 is right: "magic mushrooms" contain psilocybin, which acts on the mind; it is now being tested for depression. Statement 3 is right: some fungi make chemicals that kill insects, and others are used as biopesticides. Statement 4 is right: a few species glow in the dark through bioluminescence, including some found in the Western Ghats.
Notice the link with livelihoods: India promotes mushroom farming as a low-land, high-income crop, and the Gucchi mushroom of Kashmir has a GI tag.
Answer as per the official UPSC answer key.
Consider the following statements regarding the Indian squirrels :
- 1. They build nests by making burrows in the ground.
- 2. They store their food materials like nuts and seeds in the ground.
- 3. They are omnivorous.
How many of the above statements are correct?
Answer (b) & explanation
Two statements are correct (b). Statement 1 is wrong: Indian squirrels, such as the palm squirrel and the giant squirrel, build nests in trees, in holes or of twigs and leaves, not burrows in the ground. Statement 2 is right: they bury nuts and seeds to eat later, a habit called caching. Forgotten caches often sprout, so squirrels help spread trees. Statement 3 is right: they are omnivorous, eating insects, eggs and even small birds as well as fruits, seeds and flowers.
Notice the Indian giant squirrel (Malabar giant squirrel), the state animal of Maharashtra, and the Grizzled giant squirrel, which has a sanctuary at Srivilliputhur in Tamil Nadu. Ground squirrels that do burrow, like marmots, are a different group.
Answer as per the official UPSC answer key.
Consider the following statements :
- 1. Some microorganisms can grow in environments with temperature above the boiling point of water.
- 2. Some microorganisms can grow in environments with temperature below the freezing point of water.
- 3. Some microorganisms can grow in highly acidic environment with a pH below 3.
How many of the above statements are correct?
Answer (c) & explanation
All three statements are correct (c). These microbes are extremophiles. Statement 1 is right: some archaea near deep-sea vents grow above 100°C; water stays liquid there because of high pressure. Methanopyrus kandleri grows at up to 122°C. Statement 2 is right: psychrophiles grow below 0°C in sea ice, glaciers and permafrost, where salt keeps water liquid. Statement 3 is right: acidophiles live in acid mine water and hot springs with a pH near 1.
Notice the uses: the enzyme Taq polymerase, from a hot-spring bacterium, made the PCR test possible, which was used for COVID testing. Extremophiles also suggest where life might exist on other worlds, such as Mars or Jupiter's moon Europa.
Answer as per the official UPSC answer key.
Which one of the following makes a tool with a stick to scrape insects from a hole in a tree or a log of wood?
Answer (b) & explanation
The orangutan uses a stick as a tool (b). Orangutans, especially in Sumatra, shape sticks to pry insects and honey out of tree holes and to break open spiny fruits. Young ones learn the skill from their mothers, a sign of culture in apes. Option (d) is the trap: the sloth bear eats termites and ants, but it sucks them out of mounds through a gap in its front teeth; it makes no tool. The fishing cat (a) catches fish with its paws. Otters (c) use stones to crack shells but do not dig insects with sticks.
Notice the famous tool-users: chimpanzees "fish" for termites with stems, crows bend wires into hooks, and Egyptian vultures drop stones on eggs. Orangutans are critically endangered by palm oil plantations.
the sloth bear is famous for eating termites, which makes it tempting.
Answer as per the official UPSC answer key.
‘Aerial metagenomics’ best refers to which one of the following situations?
Answer (a) & explanation
Aerial metagenomics means collecting DNA from the air at one go (a). Animals and plants constantly shed tiny bits of DNA into the air, through skin, hair, pollen and spores. Aerial metagenomics filters air at one spot and reads all the DNA at once to list the species present, without seeing or catching them. It is part of environmental DNA (eDNA) methods. Option (b) is too narrow: it is not limited to birds. Option (c) is wrong: it does not take blood from animals. Option (d) describes drone sampling of land and water.
Notice that in 2022, scientists picked up DNA of animals in a zoo just by sampling the air. eDNA from water is already used to track fish and rare species.
"aerial" suggests birds or drones, but it refers to the air sample.
Answer as per the official UPSC answer key.
Protected areas and conservation 1
Consider the following statements :
Once the Central Government notifies an area as a ‘Community Reserve’
- 1. the Chief Wildlife Warden of the State becomes the governing authority of such forest
- 2. hunting is not allowed in such area
- 3. people of such area are allowed to collect non-timber forest produce
- 4. people of such area are allowed traditional agricultural practices
How many of the above statements are correct?
Answer (b) & explanation
Two statements are correct (b). Community reserves were added to the Wild Life (Protection) Act in 2003. They are notified on community or private land with the people's consent; note that under the Act it is the State Government, not the Centre, that notifies them. Statement 1 is wrong: a Community Reserve Management Committee runs them, not the Chief Wildlife Warden. Statement 2 is right: hunting is banned. Statement 3 is right: people may collect non-timber forest produce. Statement 4 is wrong: changes in land use, including traditional farming or jhum, are not allowed.
Notice the four types of protected areas: national parks, sanctuaries, conservation reserves and community reserves. Many community reserves are in Meghalaya and Nagaland, where communities own most forests.
"governing authority" tempts you because the Warden does run sanctuaries.
Answer as per the official UPSC answer key.
Climate change and international conventions 2
Consider the following statements :
- Statement-I : Carbon markets are likely to be one of the most widespread tools in the fight against climate change.
- Statement-II : Carbon markets transfer resources from the private sector to the State.
Which one of the following is correct in respect of the above statements?
Answer (b) & explanation
Both statements are correct but II does not explain I (b). Statement I is right: carbon markets put a price on emissions and are spreading fast, from the EU's ETS to China's national market, and the Article 6 rules under the Paris Agreement. Statement II is right: under cap-and-trade, governments sell or auction emission permits, so money moves from companies to the State. But II is not the reason for I: markets spread because they cut emissions where it is cheapest, letting firms that can cut cheaply sell their spare permits.
Notice India's own Carbon Credit Trading Scheme (2023), run by the Bureau of Energy Efficiency. It sets emission-intensity targets for heavy industries such as cement, steel and aluminium.
Answer as per the official UPSC answer key.
Consider the following activities :
- 1. Spreading finely ground basalt rock on farmlands extensively
- 2. Increasing the alkalinity of oceans by adding lime
- 3. Capturing carbon dioxide released by various industries and pumping it into abandoned subterranean mines in the form of carbonated waters
How many of the above activities are often considered and discussed for carbon capture and sequestration?
Answer (c) & explanation
All three activities are discussed for carbon removal (c). Item 1 is right: enhanced rock weathering: finely ground basalt spread on farms reacts with CO₂ in rain and soil and locks it in stable carbonates; it can also improve soil. Item 2 is right: ocean alkalinity enhancement: adding lime makes seawater more alkaline, so it absorbs more CO₂ from the air. Item 3 is right: pumping captured CO₂ underground as carbonated water is geological storage; in Iceland, the CarbFix project turns it into rock within two years.
Notice that these are carbon dioxide removal methods, needed to reach net zero, alongside cutting emissions. India's Deccan basalts make enhanced rock weathering an attractive option here.
Answer as per the official UPSC answer key.
Pollution, environmental laws and green technology 7
Consider the following :
- 1. Aerosols
- 2. Foam agents
- 3. Fire retardants
- 4. Lubricants
In the making of how many of the above are hydrofluorocarbons used?
Answer (c) & explanation
HFCs are used in three of the four (c). Hydrofluorocarbons (HFCs) replaced the ozone-depleting CFCs. Besides refrigeration and air-conditioning, they are used as aerosol propellants, as foam-blowing agents for insulation, and as fire suppressants that put out fires without water damage. Item 4 is wrong: HFCs are not used in making lubricants. So options (a), (b) and (d) fall.
Notice the twist: HFCs do not harm the ozone layer, but they are powerful greenhouse gases, often thousands of times stronger than CO₂. The Kigali Amendment (2016) to the Montreal Protocol phases them down. India, in the third group, will freeze use in 2028 and cut 85% by 2047. Its India Cooling Action Plan (2019) supports this.
Answer as per the official UPSC answer key.
With reference to the role of biofilters in Recirculating Aquaculture System, consider the following statements :
- 1. Biofilters provide waste treatment by removing uneaten fish feed.
- 2. Biofilters convert ammonia present in fish waste to nitrate.
- 3. Biofilters increase phosphorus as nutrient for fish in water.
How many of the statements given above are correct?
Answer (b) & explanation
Two statements are correct (b). A Recirculating Aquaculture System cleans and reuses the same water, so it needs far less water and land. Statement 1 is right: the biofilter treats wastes from fish droppings and uneaten feed, after solids are removed. Statement 2 is right: its bacteria turn toxic ammonia from fish waste into nitrite and then into much less harmful nitrate; this is nitrification. Statement 3 is wrong: biofilters do not raise phosphorus; fish need clean water, and extra phosphorus only feeds unwanted algae.
Notice the link with aquaponics, where the nitrate-rich water feeds plants grown alongside the fish. India's PM Matsya Sampada Yojana (2020) funds RAS and biofloc units. India is the world's second-largest fish producer.
Answer as per the official UPSC answer key.
Consider the following statements regarding mercury pollution :
- 1. Gold mining activity is a source of mercury pollution in the world.
- 2. Coal-based thermal power plants cause mercury pollution.
- 3. There is no known ‘safe level’ of exposure to mercury.
How many of the above statements are correct?
Answer (b) & explanation
Two statements are correct (b). Statement 1 is right: small-scale gold mining, which uses mercury to bind gold particles, is the largest source of mercury released by people worldwide. Statement 2 is right: coal burning, mainly in thermal power plants, comes next, as coal holds traces of mercury. Statement 3 is wrong under UPSC's key: "no known safe level" is what the WHO says about lead. For mercury, health agencies set tolerable intake limits, though they treat it as highly toxic.
Notice the Minamata Convention (2013, in force 2017), named after Japan's mercury poisoning disaster from factory waste. India has ratified it. Mercury turns into methylmercury in water and builds up in fish, harming the brain.
the phrase "no known safe level" is borrowed from lead.
Answer as per the official UPSC answer key.
With reference to green hydrogen, consider the following statements :
- 1. It can be used directly as a fuel for internal combustion.
- 2. It can be blended with natural gas and used as fuel for heat or power generation.
- 3. It can be used in the hydrogen fuel cell to run vehicles.
How many of the above statements are correct?
Answer (c) & explanation
All three statements are correct (c). Green hydrogen is made by splitting water using renewable electricity. Statement 1 is right: it can be burnt directly in a modified internal combustion engine, and trucks and buses running this way are being tested. Statement 2 is right: it can be blended with natural gas, often up to about 20%, for heating or power; India has tested this in city gas networks. Statement 3 is right: it can be used in a fuel cell, which combines hydrogen with oxygen to make electricity, emitting only water, to run vehicles.
Notice India's National Green Hydrogen Mission (2023), which aims at 5 million tonnes a year by 2030. Its main early users will be fertiliser plants, refineries and steel.
Answer as per the official UPSC answer key.
With reference to coal-based thermal power plants in India, consider the following statements :
- 1. None of them uses seawater.
- 2. None of them is set up in water-stressed district.
- 3. None of them is privately owned.
How many of the above statements are correct?
Answer (d) & explanation
None of the statements is correct (d). Statement 1 is wrong: coastal plants such as those at Mundra in Gujarat and others on the Tamil Nadu and Andhra coasts use seawater for cooling. Statement 2 is wrong: studies have found many thermal plants in water-stressed districts, and some have shut for days in droughts for lack of water. Statement 3 is wrong: large coal plants are run by private companies such as Adani Power, Tata Power and JSW, besides public firms like NTPC. All three "none" statements fail.
Notice the hint: UPSC's absolute words like "none", "all" and "only" are often wrong. Coal still gives about 70–75% of India's power, and plants must meet stricter water-use and emission norms.
"none" statements are easy to sink with one example each.
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Answer as per the official UPSC answer key.
Consider the following statements :
- 1. In India, the Biodiversity Management Committees are key to the realization of the objectives of the Nagoya Protocol.
- 2. The Biodiversity Management Committees have important functions in determining access and benefit sharing, including the power to levy collection fees on the access of biological resources within its jurisdiction.
Which of the statements given above is/are correct?
Answer (c) & explanation
Both statements are correct (c). Statement 1 is right: under the Biological Diversity Act, 2002, every local body, such as a panchayat or municipality, sets up a Biodiversity Management Committee. BMCs are key to the Nagoya Protocol's aim of fair and equitable sharing of benefits from biological resources and traditional knowledge, because they bring it down to villages. Statement 2 is right: BMCs keep the People's Biodiversity Register, are consulted on access to local resources, and may levy collection fees on those who take resources from their area.
Notice the three-tier structure: the National Biodiversity Authority in Chennai, State Biodiversity Boards and BMCs. The Act was amended in 2023 to ease rules for AYUSH practitioners and research.
Answer as per the official UPSC answer key.
Consider the following heavy industries :
- 1. Fertilizer plants
- 2. Oil refineries
- 3. Steel plants
Green hydrogen is expected to play a significant role in decarbonizing how many of the above industries?
Answer (c) & explanation
Green hydrogen can help decarbonise all three (c). Item 1 is right: fertiliser plants use hydrogen to make ammonia, the base of urea. Item 2 is right: oil refineries use hydrogen to remove sulphur from fuels and to crack heavy oils. Both now mostly use grey hydrogen made from natural gas, which releases CO₂. Switching to green hydrogen, made from water using renewable power, cuts those emissions. Item 3 is right: steel plants can use hydrogen in place of coking coal to remove oxygen from iron ore, called direct reduced iron, leaving water instead of CO₂.
Notice India's National Green Hydrogen Mission (2023) with its SIGHT incentive programme. Sweden's HYBRIT project made the first fossil-free steel, and Indian steelmakers are running pilots.
Answer as per the official UPSC answer key.
All years by topic
Every question from 2011 to 2026, grouped by syllabus topic, with year-wise trends.