Pollution & Climate Change — UPSC Prelims Science & Environment previous year questions

Statement I is a fact. India's Long-Term Low Emission Development Strategy (LT-LEDS), submitted in 2022, shows how India plans to reach net zero by 2070.
Statement II is a fact. India's 4th Biennial Update Report (BUR-4) showed about 8% fewer greenhouse gas emissions in 2020 than in 2019.
Relation 1 is correct. Statement II gives data that supports the low-carbon path in statement I.
Relation 2 is correct. Statement III demands quick, short-term cuts. This clashes with the long-term approach of the LT-LEDS.
Relation 3 is wrong. Because III contradicts I, they cannot together form a premise for long-term sustainability.
Remember: BUR is submitted to the UNFCCC every two years.

Source: UNFCCC reports; India's LT-LEDS (MoEFCC, 2022); India's BUR-4 (Dec 2024)

REDD+ stands for Reducing Emissions from Deforestation and Forest Degradation. It pays communities to protect forests and so cut carbon emissions.
The Khasi Hills Community REDD+ Project in Meghalaya is India's first Plan Vivo certified REDD+ project. It is run by Khasi community institutions.
The other options are not the first Plan Vivo certified REDD+ project in India.
So the answer is (c).
Remember: Plan Vivo is a standard for community-led carbon and nature projects.

Source: Plan Vivo Foundation project register; Meghalaya Basin Development Authority notes on Khasi Hills REDD+

Statement 1 is wrong. Hydrogen from natural gas reforming with carbon capture and storage is called blue hydrogen, not green.
Statement 2 is correct. Green hydrogen is made by splitting water by electrolysis, using renewable electricity.
Statement 3 is correct. India's National Green Hydrogen Mission aims to avoid about 50 million tonnes of greenhouse gas emissions every year by 2030.
So 2 and 3 only.
Remember: grey hydrogen comes from fossil fuel with no capture; the Mission target is 5 MMT of green hydrogen a year by 2030.

Source: Ministry of New and Renewable Energy, National Green Hydrogen Mission (2023)

All three statements are correct, and Statements II and III both explain Statement I.
A circular economy keeps materials in use through reuse, repair and recycling.
Statement II is correct. It needs fewer fresh raw materials. Less mining and processing means lower emissions.
Statement III is correct. It cuts waste in production. Less waste means less energy use and less methane from landfills.
Both reasons explain the lower emissions in Statement I. Option (a) fits.
Remember: Circular economy aims to keep resources in use for as long as possible.

Source: UNEP and Ellen MacArthur Foundation material on circular economy; Government of India circular economy policy papers

Statement I is correct. Cement making gives about 7 to 8 per cent of global carbon dioxide emissions. This is more than 5 per cent.
Statement II is correct. Limestone is mixed with silica-bearing clay. The clay supplies silica, alumina and iron.
Statement III is correct. In the kiln, limestone (calcium carbonate) breaks down into lime and carbon dioxide during clinker production.
Only Statement III explains Statement I. The carbon dioxide released in this step is the main source of process emissions. Statement II only describes raw materials. Option (b) fits.
Remember: Calcination of limestone causes roughly 60 per cent of cement's CO2 emissions.

Source: International Energy Agency and Global Cement and Concrete Association studies on cement emissions

Statement I is correct. India did not sign the COP28 Declaration on Climate and Health.
Statement II is incorrect. The Declaration is voluntary and non-binding. Signing it does not make decarbonising the health sector mandatory.
Statement III is treated as correct in UPSC's key. The concern is that decarbonising the health sector could weaken the resilience of India's health-care system. This explains India's decision not to sign.
So only one of Statements II and III is correct, and it explains Statement I. Option (c) fits.
Remember: COP28 was held in Dubai in 2023.

Source: COP28 (Dubai, 2023) Declaration on Climate and Health; Ministry of Health and Family Welfare statements

Statement I is correct. Article 6 of the Paris Agreement is widely discussed in climate talks.
Statement II is correct. Articles 6.2 and 6.4 set principles for carbon markets, including the international transfer of credits.
Statement III is correct. Article 6.8 promotes non-market approaches between countries to reach their climate targets.
Both statements explain why Article 6 is discussed so often. Option (a) fits.
Remember: Article 6.2 covers bilateral trading of mitigation outcomes. Article 6.4 creates a UN-supervised crediting mechanism.

Source: Paris Agreement (2015), Article 6; UNFCCC material on carbon markets

All three statements are correct.
Statement I: Captured carbon dioxide can be stored underground. This is carbon sequestration.
Statement II: It can be used as raw material for plastics and in food processing, such as carbonated drinks.
Statement III: In aviation, the captured carbon can be combined with hydrogen to make synthetic low-carbon fuel.
So I, II and III are correct.
Remember: Direct air capture pulls CO2 from ambient air. Ordinary carbon capture takes it from factory exhaust.

Source: International Energy Agency, Direct Air Capture report

Statement I is incorrect. India's emissions are about 2 tonnes of CO2 per person. This is far above 0.5 tonnes.
Statement II is correct. For CO2 from fuel combustion, India ranks second in the Asia-Pacific region, after China.
Statement III is correct. Electricity and heat producers are the largest source of India's CO2 emissions because of coal power.
So II and III are correct.
Remember: India's per-capita emissions are still below the world average.

Source: International Energy Agency, CO2 Emissions reports (India)

All three items contain plastic.
Cigarette butts have filters made of cellulose acetate. This is a plastic.
Eyeglass lenses are mostly made of polycarbonate or similar plastics.
Car tyres contain synthetic rubber, which is a polymer. They also shed microplastics as they wear.
So the answer is all the three.
Remember: Tyre wear is a major source of microplastics in the environment.

Source: UNEP reports on plastic pollution; Central Pollution Control Board material on microplastics

Both statements are correct, as per UPSC's key.
A wet-bulb temperature of 35 degrees Celsius is the limit of human survival. At that point the body cannot lose heat through sweating. Humans and animals then suffer severe heat stress.
Statement II describes this directly, so it is correct.
Statement I is also accepted as an implication. Rising heat is linked to more floods, cyclones and droughts in peninsular India.
So the answer is both I and 2.
Remember: Wet-bulb temperature combines heat and humidity.

Source: World Bank report on India's cooling sector; IPCC reports on humid heat

Statement 1 is correct. PFAS are used in non-stick pans, food wrappers and fabrics. They have been found in drinking water and food.
Statement 2 is correct. Their carbon–fluorine bond is very strong. So they resist breakdown and are called 'forever chemicals'.
Statement 3 is correct. Because they persist, they build up in the bodies of animals and people.
So all three are correct.
Remember: PFAS are covered by the Stockholm Convention process for persistent organic pollutants.

Source: US EPA / WHO fact sheets on PFAS; Stockholm Convention on POPs

Statement 1 is correct. Artisanal gold mining uses mercury to extract gold and releases it into air and water.
Statement 2 is correct. Coal contains traces of mercury, which escapes when coal is burnt in power plants.
Statement 3 is correct. WHO states that there is no known safe level of mercury exposure, since it harms the nervous system.
Remember: The Minamata Convention is the treaty on mercury.

Source: WHO fact sheet on mercury; Minamata Convention on Mercury

Hydrofluorocarbons (HFCs) are man-made gases that replaced ozone-depleting CFCs.
They are used as propellants in aerosols.
They are used as blowing agents in making foams.
They are used as clean fire-suppression agents (fire retardants).
They are not used as lubricants.
So three of the four uses are valid.
HFCs do not harm ozone but are strong greenhouse gases. The Kigali Amendment (2016) to the Montreal Protocol phases them down.

Source: Previous year paper; answer key cross-checked against published sources

Statement 1 is correct. PET is a polyester fibre and is blended with cotton and wool to add strength.
Statement 2 is incorrect. PET is not suited to every alcoholic drink, as strong spirits can affect it.
Statement 3 is correct. PET bottles are widely recycled into fibre and new products.
Statement 4 is incorrect. Burning PET releases carbon dioxide, a greenhouse gas.
So statements 1 and 3 are correct.
Remember: PET carries recycling code 1.

Source: Bureau of Indian Standards / CPCB plastic waste guidance; NCERT Class XII Chemistry, Ch. 15 Polymers

Pair 1 is incorrect. Annex-I countries are the industrialised countries listed under the UNFCCC and the Kyoto Protocol. The Cartagena Protocol deals with biosafety.
Pair 2 is incorrect. Certified Emission Reductions are credits earned under the Kyoto Protocol. The Nagoya Protocol deals with access and benefit sharing of genetic resources.
Pair 3 is correct. The Clean Development Mechanism is one of the three flexibility mechanisms of the Kyoto Protocol.
Remember: The other two Kyoto mechanisms are Emissions Trading and Joint Implementation.

Source: Kyoto Protocol (1997), Arts. 6, 12, 17

Chlorofluorocarbons release chlorine in the stratosphere, which destroys ozone: A-2.
Sulphur dioxide forms sulphuric acid in the air and causes acid rain: B-1.
Lead compounds damage the nervous system: C-3.
Carbon dioxide is the largest contributor to the greenhouse effect: D-4.
So the code is 2 1 3 4.

Source: NCERT Class XI Chemistry, Environmental Chemistry; NCERT Class X Science, Our Environment

Noise limits are set by the Noise Pollution (Regulation and Control) Rules, 2000.
Daytime limits are: silent zone 50 dB, residential 55 dB, commercial 65 dB, industrial 75 dB.
So A matches 2 (55 dB) and B matches 1 (50 dB).
D matches 3 (65 dB).
C matches 4, the highest value in the list; the rules give 75 dB, but 70 dB is the closest listed.
This gives the code 2 1 4 3.
Remember: Daytime is 6 am to 10 pm; night limits are 10 dB lower for most zones.

Source: Noise Pollution (Regulation and Control) Rules, 2000

Option (a) is correctly matched. The Cartagena Protocol regulates movement of living modified organisms.
Option (b) is correctly matched. The Stockholm Convention bans or restricts persistent organic pollutants.
Option (c) is correctly matched. The Montreal Protocol phases out ozone-depleting substances.
Option (d) is wrongly matched. The Kyoto Protocol limits greenhouse gas emissions. It is not about saving water.
Remember: The Montreal Protocol was adopted in 1987.

Source: Respective treaty texts

Mercury poisoning caused Minamata disease in Japan. This match is correct.
Cadmium caused Itai-Itai disease, which weakens bones. This match is correct.
Nitrate in drinking water causes methemoglobinemia, called blue baby syndrome. This match is correct.
Excess fluoride causes fluorosis, which damages teeth and bones. It does not cause indigestion, so this match is wrong.
Remember: Fluorosis is common in Telangana, Andhra Pradesh and Rajasthan groundwater.

Source: NCERT Class XII Biology, Environmental Issues; WHO fact sheets on fluoride