Question 1

With reference to the planet Earth, consider the following statements:
I. Rain forests produce more oxygen than that produced by oceans.
II. Marine phytoplankton and photosynthetic bacteria produce about 50% of world's oxygen.
III. Well-oxygenated surface water contains several folds higher oxygen than that in atmospheric air.
Which of the statements given above is/are correct?

Accepted Answer

II only — Marine phytoplankton and photosynthetic bacteria together produce roughly half the world's oxygen; rain forests do not out-produce oceans, and dissolved oxygen in surface water is actually far less concentrated than atmospheric oxygen.

Question 2

"If rainforests and tropical forests are the lungs of the Earth, then surely wetlands function as its kidneys." Which one of the following functions of wetlands best reflects the above statement?

Accepted Answer

Aquatic plants absorb heavy metals and excess nutrients. — Kidneys filter toxins from the blood; similarly, wetland plants absorb heavy metals and excess nutrients, acting as natural filters that purify water passing through.

Question 3

Consider the following kinds of organisms:
1) Copepods
2) Cyanobacteria
3) Diatoms
4) Foraminifera
Which of the above are primary producers in the food chains of oceans?

Accepted Answer

2 and 3 — Cyanobacteria and diatoms are photosynthetic organisms and thus primary producers; copepods are zooplankton (consumers) and foraminifera are heterotrophic protists.

Question 4

In case of which one of the following biogeochemical cycles the weathering of rocks is the main source of release of nutrient to enter the cycle?

Accepted Answer

Phosphorus cycle — Phosphorus has no significant atmospheric reservoir; it enters the cycle primarily through the weathering of phosphate-containing rocks.

Question 5

Which of the following are detritivores?
1) Earthworms
2) Jellyfish
3) Millipedes
4) Seahorses
5) Woodlice
Select the correct answer using the code given below.

Accepted Answer

1, 3 & 5 only — Earthworms, millipedes, and woodlice are classic detritivores that break down dead organic matter; jellyfish are carnivorous predators and seahorses feed on live crustaceans.

Question 6

Due to some reasons, if there is a huge fall in the population of species of butterflies, what could be its likely consequence/consequences?
1. Pollination of some plants could be adversely affected.
2. There could be a drastic increase in the fungal infections of some cultivated plants.
3. It could lead to a fall in the population of some species of wasps, spiders and birds.
Select the correct answer using the code given below:

Accepted Answer

1 and 3 only — Butterflies are important pollinators (consequence 1) and also prey for wasps, spiders, and birds (consequence 3); there is no established link between butterfly decline and increased fungal infections of plants.

Question 7

Consider the following:
I. Cigarette butts
II. Eyeglass lenses
III. Car tyres
How many of them contain plastic?

Accepted Answer

All the three — All three, cigarette butts (cellulose acetate filter), eyeglass lenses (polycarbonate or acrylic), and car tyres (synthetic rubber compounds), contain plastic materials.

Question 8

Artificial way of causing rainfall to reduce air pollution makes use of

Accepted Answer

silver iodide and potassium iodide — Cloud seeding to induce artificial rainfall uses silver iodide as the primary nucleating agent along with potassium iodide to promote ice crystal formation.

Question 9

Consider the following statements:
Statement I: Activated carbon is a good and an attractive tool to remove pollutants from effluent streams and to remediate contaminants from various industries.
Statement II: Activated carbon exhibits a large surface area and a strong potential for adsorbing heavy metals.
Statement III: Activated carbon can be easily synthesized from environmental wastes with high carbon content.
Which one of the following is correct in respect of the above statements?

Accepted Answer

Both Statement II and Statement III are correct and both of them explain Statement I — Activated carbon's large surface area (Statement II) and its synthesisability from carbon-rich waste (Statement III) together explain why it is effective for removing pollutants from effluents (Statement I).

Question 10

According to the Environmental Protection Agency (EPA), which one of the following is the largest source of Sulphur dioxide emissions?

Accepted Answer

Power plants using fossil fuels — Fossil-fuel-burning power plants are the single largest source of SO₂ emissions because they combust large quantities of sulphur-containing coal and oil continuously.

Question 11

With reference to Perfluoroalkyl and polyfluoroalkyl substances (PFAS) that are used in making many consumer products, consider the following statements:
1. PFAS are found to be widespread in drinking water, food and food packaging materials.
2. PFAS are not easily degraded in the environment.
3. Persistent exposure to PFAS can lead to bioaccumulation in animal bodies.
Which of the statements given above are correct?

Accepted Answer

1, 2 and 3 — PFAS are persistent 'forever chemicals' that contaminate water and food, resist degradation, and bioaccumulate in living organisms, all three statements are correct.

Question 12

'Membrane Bioreactors' are often discussed in the context of:

Accepted Answer

Wastewater treatment technologies — Membrane bioreactors (MBRs) combine biological treatment with membrane filtration for advanced wastewater treatment, removing contaminants more efficiently than conventional methods.

Question 13

Consider the following statements:
Statement I: Many chewing gums found in the market are considered a source of environmental pollution.
Statement-II: Many chewing gums contain plastic as gum base.
Which one of the following is correct in respect of the above statements?

Accepted Answer

Statement-I and Statement-II are correct and Statement-II explains Statement-I — Many commercial chewing gums use polyvinyl acetate or other synthetic polymers as gum base, making them a plastic-based environmental pollutant, Statement II directly explains Statement I.

Question 14

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?

Accepted Answer

All three — All three are correct: artisanal gold mining uses mercury amalgamation, coal burning releases mercury, and medical consensus holds that no safe threshold exists for mercury exposure.

Question 15

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?

Accepted Answer

Only two — Biofilters in RAS convert toxic ammonia to less harmful nitrate (statement 2 correct) through nitrification, but they do not remove uneaten feed (physical filters do that) nor increase phosphorus.

Question 16

Consider the following:
1. Carbon monoxide
2. Nitrogen oxide
3. Ozone
4. Sulphur dioxide
Excess of which of the above in the environment is/are the cause(s) of acid rain?

Accepted Answer

2 and 4 only — Acid rain is primarily caused by nitrogen oxides (NOx) and sulphur dioxide (SO₂), which react with atmospheric water to form nitric and sulphuric acids respectively.

Question 17

Consider the following statements:
1. Other than those made by humans, nanoparticles do not exist in nature.
2. Nanoparticles of some metallic oxides are used in the manufacture of some cosmetics.
3. Nanoparticles of some commercial products which enter the environment are unsafe for humans.
Which of the statements given above is/are correct?

Accepted Answer

2 and 3 — Natural nanoparticles exist (e.g., from volcanic eruptions), so statement 1 is wrong; metallic oxide nanoparticles like titanium dioxide are widely used in sunscreens and cosmetics, and some engineered nanoparticles pose environmental health risks.

Question 18

In the context of WHO Air Quality Guidelines, consider the following statements:
1. The 24-hour mean of PM 2.5 should not exceed 15 µg/m3 and annual mean of PM2.5 should not exceed 5 µg/m3.
2. In a year, the highest levels of ozone pollution occur during the periods of inclement weather.
3. PM 10 can penetrate the lung barrier and enter the bloodstream.
4. Excessive ozone in the air can trigger asthma.
Which of the statements given above are correct?

Accepted Answer

1 and 4 only — WHO guidelines set PM2.5 annual mean at 5 µg/m3 and 24-hr mean at 15 µg/m3 (statement 1 correct); ozone peaks in sunny weather not inclement weather (2 wrong); PM2.5 not PM10 penetrates into bloodstream (3 wrong); ozone does trigger asthma (4 correct).

Question 19

Why is there a concern about copper smelting plants?
1) They may release lethal quantities of carbon monoxide into environment.
2) The copper slag can cause the leaching of some heavy metals into environment.
3) They may release sulphur dioxide as a pollutant.
Select the correct answer using the code given below.

Accepted Answer

2 and 3 only — Copper smelting releases SO₂ (from sulphide ores) and produces slag that can leach heavy metals into soil and water, but CO releases are not the primary concern in copper smelting.

Question 20

Magnetite particles suspected to cause neurodegenerative problems, are generated as environmental pollutants from which of the following?
1) Brakes of motor vehicles
2) Engines of motor vehicles
3) Microwave stoves within homes
4) Power plants
5) Telephone lines
Select the correct answer using the code given below.

Accepted Answer

1, 2 and 4 only — Magnetite nanoparticles are emitted by friction in vehicle brakes, combustion in vehicle engines, and coal-burning power plants, microwave stoves and telephone lines do not generate them.

Question 21

With reference to furnace oil, consider the following statements:
1) It is a product of oil refineries.
2) Some industries use it to generate power.
3) Its use causes sulphur emissions into environment.
Which of the statements given above are correct?

Accepted Answer

1, 2 and 3 — Furnace oil is a heavy residual product from oil refining, used as industrial fuel, and it contains significant sulphur that is released as SO₂ upon combustion, all three statements are correct.

Question 22

Consider the following statements:
1. Coal ash contains arsenic, lead and mercury.
2. Coal-fired power plants release sulphur dioxide and oxides of nitrogen into the environment.
3. High ash content is observed in Indian coal.
Which of the statements given above is/are correct?

Accepted Answer

1, 2 and 3 — Indian coal is known for high ash content; coal ash contains toxic trace metals including arsenic, lead, and mercury; and coal combustion releases SO₂ and NOx, all three statements are correct.

Question 23

Which of the following are the reasons/factors for exposure to benzene pollution?
1. Automobile exhaust
2. Tobacco smoke
3. Wood burning
4. Using varnished wooden furniture
5. Using products made of polyurethane
Select the correct answer using the code given below:

Accepted Answer

1, 2 and 3 only — Automobile exhaust, tobacco smoke, and wood burning are established sources of benzene exposure; varnished furniture and polyurethane products are not significant benzene emission sources.

Question 24

Steel slag can be the material for which of the following?
1. Construction of base road
2. Improvement of agricultural soil
3. Production of cement
Select the correct answer using the code given below:

Accepted Answer

1, 2 and 3 — Steel slag is a versatile industrial by-product used in road base construction, as a soil conditioner in agriculture, and as a partial replacement for clinker in cement production.

Question 25

In the context of proposals to the use of hydrogen-enriched CNG (H-CNG) as fuel for buses in public transport, consider the following statements:
1. The main advantage of the use of H-CNG is the elimination of carbon monoxide emissions.
2. H-CNG as fuel reduces carbon dioxide and hydrocarbon emissions.
3. Hydrogen up to one-fifth by volume can be blended with CNG as fuel for buses.
4. H-CNG makes the fuel less expensive than CNG.
Which of the statements given above is/are correct?

Accepted Answer

2 and 3 only — H-CNG reduces CO2 and hydrocarbon emissions and the standard blend is up to 18–20% hydrogen by volume; it does not eliminate CO emissions entirely and hydrogen addition typically raises cost.

Question 26

Consider the following:
1. Carbon monoxide
2. Methane
3. Ozone
4. Sulphur dioxide
Which of the above are released into atmosphere due to the burning of crop/biomass residue?

Accepted Answer

1, 2, 3 and 4 — Burning crop residue releases CO (incomplete combustion), methane (from smouldering), SO2 (from sulphur in biomass), and also generates ground-level ozone via photochemical reactions with emitted precursors.

Question 27

Why is there a great concern about the 'microbeads' that are released into environment?

Accepted Answer

They are considered harmful to marine ecosystems. — Microbeads are tiny plastic particles from personal care products that pass through water filters, enter waterways, and are ingested by marine organisms, causing significant harm to marine ecosystems.

Question 28

Consider the following statements:
1. Agricultural soils release nitrogen oxides into the environment.
2. Cattle release ammonia into the environment.
3. Poultry industry releases reactive nitrogen compounds into the environment.
Which of the statements given above is/are correct?

Accepted Answer

1, 2 and 3 — All three are correct: soils emit N2O/NO from nitrification/denitrification, cattle excreta release ammonia, and poultry litter releases ammonia and other reactive nitrogen compounds.

Question 29

In India, the use of carbofuran, methyl parathion, phorate and triazophos is viewed with apprehension. These chemicals are used as:

Accepted Answer

Pesticides in agriculture — Carbofuran, methyl parathion, phorate, and triazophos are all organophosphate or carbamate pesticides used in agriculture that are highly toxic and subject to regulatory concern.

Question 30

Biological Oxygen Demand (BOD) is a standard criterion for:

Accepted Answer

Pollution assay in aquatic ecosystems — BOD measures the amount of dissolved oxygen consumed by biological processes in water, making it a standard indicator of organic pollution levels in aquatic ecosystems.

Question 31

Consider the following statements:
I. Carbon dioxide (CO₂) emissions in India are less than 0.5 t CO₂/capita.
II. In terms of CO₂ emissions from fuel combustion, India ranks second in Asia-Pacific region.
III. Electricity and heat producers are the largest sources of CO₂ emissions in India.
Which of the statements given above is/are correct?

Accepted Answer

II and III only — India's per-capita CO2 emissions exceed 0.5 t (Statement I is wrong), but India does rank second in Asia-Pacific for fuel combustion emissions and the power sector (electricity and heat producers) is indeed the largest emitter.

Question 32

The World Bank warned that India could become one of the first places where wet-bulb temperatures routinely exceed 35 °C. Which of the following statements best reflect(s) the implication of the above-said report?
I. Peninsular India will most likely suffer from flooding, tropical cyclones and droughts.
II. The survival of animals including humans will be affected as shedding of their body heat through perspiration becomes difficult.
Select the correct answer using the code given below.

Accepted Answer

II only — A wet-bulb temperature above 35°C directly impairs evaporative cooling (sweating), threatening survival, that is the specific implication; flooding and cyclones are unrelated to wet-bulb temperature thresholds.

Question 33

Consider the following statements:
Statement I: Studies indicate that carbon dioxide emissions from cement industry account for more than 5% of global carbon emissions.
Statement II: Silica-bearing clay is mixed with limestone while manufacturing cement.
Statement III: Limestone is converted into lime during clinker production for cement manufacturing.
Which one of the following is correct in respect of the above statements?

Accepted Answer

Both Statement II and Statement III are correct but only one of them explains Statement I — Both Statements II and III are factually correct about cement manufacturing, but only the conversion of limestone to lime (Statement III) directly releases CO2 and thus explains the high emissions figure in Statement I.

Question 34

Which organization has enacted the Nature Restoration Law (NRL) to tackle climate change and biodiversity loss?

Accepted Answer

The European Union — The European Union passed the Nature Restoration Law in 2024 as part of its Green Deal, setting legally binding targets to restore degraded ecosystems across member states.

Question 35

Consider the following statements:
Statement I: At the 28th United Nations Climate Change Conference (COP28), India refrained from signing the "Declaration on Climate and Health".
Statement II: The COP28 Declaration on Climate and Health is a binding declaration; and if signed, it becomes mandatory to decarbonize health sector.
Statement III: If India's health sector is decarbonized, the resilience of its health-care system may be compromised.
Which one of the following is correct in respect of the above statements?

Accepted Answer

Only one of the Statements II and III is correct and that explains Statement I — The COP28 Declaration on Climate and Health is a non-binding pledge, so Statement II is incorrect; Statement III (health system resilience concern) is the correct and sole explanation for India's decision not to sign.

Question 36

Which one of the following launched the 'Nature Solutions Finance Hub for Asia and the Pacific'?

Accepted Answer

The Asian Development Bank (ADB) — The Asian Development Bank (ADB) launched the Nature Solutions Finance Hub for Asia and the Pacific to mobilise finance for nature-based solutions in the region.

Question 37

Consider the following statements:
Statement I: Circular economy reduces the emissions of greenhouse gases.
Statement II: Circular economy reduces the use of raw materials as inputs.
Statement III: Circular economy reduces wastage in the production process.
Which one of the following is correct in respect of the above statements?

Accepted Answer

Both Statement II and Statement III are correct and both of them explain Statement I — A circular economy reduces raw material inputs and minimises wastage, both of which together cut greenhouse gas emissions, making Statements II and III correct and both explanatory of Statement I.

Question 38

Consider the following statements:
Statement I: Article 6 of the Paris Agreement on climate change is frequently discussed in global discussions on sustainable development and climate change.
Statement II: Article 6 of the Paris Agreement on climate change sets out the principles of carbon markets.
Statement III: Article 6 of the Paris Agreement on climate change intends to promote inter-country non-market strategies to reach their climate targets.
Which one of the following is correct in respect of the above statements?

Accepted Answer

Both Statement II and Statement III are correct and both of them explain Statement I✓ Answer
Both Statement II and Statement III are correct but only one of them explains Statement I
Only one of the Statements II and III is correct and that explains Statement I
Neither Statement II nor Statement III is correct

Why

A circular economy reduces raw material inputs and minimises wastage, both of which together cut greenhouse gas emissions, making Statements II and III correct and both explanatory of Statement I.

Question 39

With reference to Direct Air Capture, an emerging technology, which of the following statements is/are correct?
I. It can be used as a way of carbon sequestration.
II. It can be a valuable approach for plastic production and in food processing.
III. In aviation, it can be a source of carbon for combining with hydrogen to create synthetic low-carbon fuel.
Select the correct answer using the code given below.

Accepted Answer

I, II and III — Direct Air Capture technology can sequester carbon, supply CO2 for industrial uses like plastics and food (carbonation), and produce synthetic e-fuels for aviation when combined with green hydrogen, making all three statements correct.

Question 40

Consider the following statements:
Statement I: The European Parliament approved the Net-Zero Industry Act recently.
Statement II: The European Union intends to achieve carbon neutrality by 2040 and therefore aims to develop all of its own clean technology by that time.
Which one of the following is correct in respect of the above statements?

Accepted Answer

Statement-I is correct, but Statement-II is incorrect — While the European Parliament did approve the Net-Zero Industry Act, the EU's carbon neutrality target is 2050 (not 2040), and the Act does not require all clean technology to be developed domestically.

Question 41

One of the following regions has the world's largest tropical peatland, which holds about three years' worth of global carbon emissions from fossil fuels; and the possible destruction of which can exert detrimental effect on the global climate. Which one of the following denotes that region?

Accepted Answer

Congo Basin — The Congo Basin in Central Africa hosts the world's largest tropical peatland (the Cuvette Centrale), storing vast amounts of carbon whose release would significantly accelerate global warming.

Question 42

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?

Accepted Answer

All three — All three are recognised carbon dioxide removal or sequestration techniques: enhanced rock weathering, ocean alkalinity enhancement, and geological carbon storage as carbonated water.

Question 43

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 market transfer resources from private sector to the State.
Which of the following is correct in respect of the above statements?

Accepted Answer

Both Statement-I and Statement-II are correct and Statement-II is the correct explanation for Statement-I
Both Statement-I and Statement-II are correct and Statement-II is not the correct explanation for Statement-I
Statement-I is correct but Statement-II is incorrect✓ Answer
Statement-I is incorrect but Statement-II is correct

Why

Marsupials are indeed not found naturally in India (Statement-I is correct), but they are not restricted to montane grasslands, they thrive in diverse habitats in Australia (Statement-II is incorrect).

Question 44

Consider the following statements:
1. "The Climate Group" is an international non-profit organization that drives climate action by building large networks and runs them.
2. The International Energy Agency in partnership with the Climate Group launched a global initiative "EP100".
3. EP100 brings together leading companies committed to driving innovation in energy efficiency and increasing competitiveness while delivering on emission reduction goals.
4. Some Indian companies are members of EP100.
5. The International Energy Agency is the Secretariat to the "Under2 Coalition".
Which of the statements given above are correct?

Accepted Answer

1, 3 and 4 only — EP100 was launched by The Climate Group (not IEA), and The Climate Group (not IEA) is secretariat to the Under2 Coalition; statements 1, 3, and 4 are correct.

Question 45

"Climate Action Tracker" which monitors the emission reduction pledges of different countries is a:

Accepted Answer

Database created by coalition of research organisations — Climate Action Tracker is an independent scientific analysis run by Climate Analytics and NewClimate Institute, tracking government climate action against Paris Agreement goals.

Question 46

Among the following crops, which one is the most important anthropogenic source of both methane and nitrous oxide?

Accepted Answer

Rice — Paddy (rice) cultivation produces methane under anaerobic flooded conditions and also releases nitrous oxide when nitrogen fertilisers are applied, making it the leading agricultural source of both greenhouse gases.

Question 47

With reference to the New York declaration on Forests, which of the following statements are correct?
1. It was first endorsed at the United Nations Climate Summit in 2014.
2. It endorses a global timeline to end the loss of forests.
3. It is a legally binding international declaration.
4. It is endorsed by governments, big companies and indigenous communities.
5. India was one of the signatories at its inception.
Select the correct answer using the code given below.

Accepted Answer

1, 2 and 4 — The New York Declaration on Forests (2014) is a voluntary (non-binding) commitment endorsed by governments, companies, and indigenous groups at the UN Climate Summit, with a goal to halt deforestation by 2030.

Question 48

The 'Common Carbon Metric', supported by UNEP, has been developed for:

Accepted Answer

Assessing the carbon footprint of building operations around the world — The UNEP-supported Common Carbon Metric provides a standardised framework for measuring and reporting carbon emissions from building operations globally.

Question 49

What is blue carbon?

Accepted Answer

Carbon captured by oceans and coastal ecosystems — Blue carbon refers to the carbon stored and sequestered by marine and coastal ecosystems such as mangroves, seagrasses, and salt marshes.

Question 50

Which of the following statements best describes the term 'Social Cost of Carbon'? It is a measure, in monetary value, of the

Accepted Answer

Long-term damage done by a tonne of CO2 emissions in a given year. — The Social Cost of Carbon is an economic estimate of the net present value of harms caused by emitting one additional tonne of CO2, used to guide climate policy cost-benefit analysis.

UPSC Environment — previous-year questions

Ecosystem

Environmental Issues

Climate Change and the International Response

Biodiversity and Conservation

Organisms and Populations

Ozone Depletion and the Montreal Protocol

Environmental Governance in India

Sustainable Development and the SDGs