Pollution & waste

Answer: (a) Both Statement II and Statement III are correct and both of them explain Statement I

A circular economy keeps materials in use through reuse, repair and recycling instead of the 'take–make–dispose' model. Using fewer fresh raw materials cuts the energy spent extracting and processing them, and cutting waste cuts the emissions from producing and disposing of it, so both II and III explain the fall in greenhouse gas emissions.

• ✓ Statement-I The European Parliament lists a reduction in total annual greenhouse gas emissions among the benefits of a circular economy.
• ✓ Statement-II Reusing and recycling products slows the use of natural resources, so fewer virgin raw materials are needed; this lowers emissions from mining and processing.
• ✓ Statement-III Better design and efficient production reduce waste and the energy and resources consumed, which also lowers emissions.

Remember · Circular economy = reduce, reuse, repair, recycle. Fewer raw materials and less waste mean less energy use and lower greenhouse gas emissions.

Question and answer: UPSC's official GS Paper I (2025, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (c) All the three

All three contain plastic. Cigarette filters are made mainly of cellulose acetate fibres, which are microplastics; many eyeglass lenses are plastic (for example CR-39 and polycarbonate); and tiny plastic particles are shed by car tyres as they wear.

• ✓ I The WHO Framework Convention on Tobacco Control Secretariat says cigarette filters are mainly composed of microplastics known as cellulose acetate fibres.
• ✓ II Many spectacle lenses are made of plastic: a peer-reviewed study of spectacle lens materials covers CR-39, polycarbonate and Trivex, and calls CR-39 lenses the most basic form of plastic lenses.
• ✓ III IUCN counts particles worn off car tyres among the tiny plastic particles that reach the oceans.

Remember · Cigarette filters (cellulose acetate), eyeglass lenses (CR-39, polycarbonate) and car tyres (which shed microplastics) all contain plastic.

Question and answer: UPSC's official GS Paper I (2025, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 1 Oct 2026 (how we verify). Permalink · Report an error

Answer: (a) Both Statement II and Statement III are correct and both of them explain Statement I

Both Statement II and Statement III are correct, and both explain Statement I. A large surface area lets activated carbon hold heavy metals and other pollutants on its surface, and because it can be made cheaply from carbon-rich waste, it becomes an attractive tool for cleaning effluents.

• ✓ II Activated carbon is highly porous, with a very large surface area and strong adsorption capacity. Pollutants stick to that surface (adsorption), which is exactly how it strips heavy metals from wastewater. This explains why it removes pollutants (Statement I).
• ✓ III Farm and other carbon-rich wastes are the usual raw material for activated carbon, and the process is simple and cheap. This low cost explains why it is 'attractive' as a treatment tool (Statement I).
• ✗ (b) This option says only one of II and III explains Statement I. But the ability to adsorb (II) explains the 'good' part and the cheap, waste-based supply (III) explains the 'attractive' part, so both explain it.
• ✗ (d) Both statements are supported by published research on biomass-derived activated carbon, so 'neither is correct' fails.

Remember · Activated carbon = porous, huge surface area, strong adsorbent, cheaply made from carbon-rich waste; hence widely used to clean effluents.

Question and answer: UPSC's official GS Paper I (2025, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (a) silver iodide and potassium iodide

Artificial rain is made by cloud seeding: seed particles are added to a cloud so that rain can form, and Delhi has trialled it as an emergency measure against pollution episodes. India's IITM names silver iodide as the standard seeding agent for cold clouds, and UPSC's key pairs it with potassium iodide.

• ✓ (a) Both agents are iodides. IITM's CAIPEEX pages name silver iodide (AgI) as the ice-nucleating agent used in glaciogenic seeding; UPSC's key names potassium iodide as the second agent, which the IITM pages do not mention.
• ✗ (b) Silver nitrate replaces silver iodide here; the key's answer has both agents as iodides.
• ✗ (c) Potassium nitrate replaces potassium iodide here; the key's answer has both agents as iodides.
• ✗ (d) Silver nitrate and potassium chloride replace both iodides.

Remember · Cloud seeding uses iodide salts, chiefly silver iodide (with potassium iodide in the key), to trigger rain.

Question and answer: UPSC's official GS Paper I (2025, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (d) 1, 2 and 3

PFAS are man-made fluorinated chemicals used for non-stick, stain-proof and grease-proof products. Their carbon–fluorine bonds make them extremely persistent ('forever chemicals'), so they spread through water, food and packaging and build up in the bodies of people and animals. All three statements hold.

• ✓ 1. PFAS turn up in drinking water, in foods such as fish and dairy, and in grease-resistant food packaging like fast-food wrappers and pizza boxes.
• ✓ 2. They are long-lasting chemicals whose components break down very slowly, so they persist in the environment.
• ✓ 3. Because they persist, many PFAS are found in the blood of people and animals worldwide, and some accumulate in the body over time.

Remember · PFAS = 'forever chemicals': very slow to break down, found in water, food and packaging, and accumulate in human and animal bodies.

Question and answer: UPSC's official GS Paper I (2024, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (a) Both Statement-I and Statement-II are correct and Statement-II explains Statement-I

The chewy part of most modern gum is not a natural tree gum but a synthetic 'gum base' made of polymers such as polyvinyl acetate, polyethylene and butyl rubber, which are plastics. Because that base does not biodegrade, spat-out gum stays on pavements for years and slowly breaks into microplastics, so the plastic base is exactly why gum is counted as a pollutant.

• ✓ Statement-I Discarded gum is treated as litter, for example under the UK Clean Neighbourhoods and Environment Act, because a synthetic gum base does not biodegrade. It hardens on pavements, is costly to scrape off, and over years breaks into microplastic fragments.
• ✓ Statement-II Traditional gum used chicle, the latex of the sapodilla (zapota) tree. FSSAI's standard now permits both natural and synthetic gum bases, including synthetic rubber latex, synthetic resin and polyvinyl acetate, and US food rules list polyethylene, polyisobutylene and polyvinyl acetate. The plastic base is exactly why the gum lasts as litter, so Statement-II explains Statement-I.

Remember · Modern gum base = synthetic polymers (polyvinyl acetate, polyethylene, butyl rubber), i.e. plastic; old gum base = chicle from the zapota tree. Non-biodegradable, so gum litter becomes microplastic.

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Answer: (d) Wastewater treatment technologies

A membrane bioreactor (MBR) is a sewage and industrial-effluent treatment system. It joins the usual biological step, in which microbes break down organic waste, with fine membrane filtration that holds back solids and bacteria, so it produces clean, reusable water from a much smaller plant than conventional settling tanks.

• ✓ (d) The US EPA describes MBRs as a secondary-treatment technology for municipal wastewater that combines a suspended-growth biological reactor with microfiltration, removing nitrogen, phosphorus, bacteria and organic load.
• ✗ (c) Vaccine and biologics production uses bioreactors (fermenters) too, but the term 'membrane bioreactor' refers to the filtration-based wastewater process.
• ✗ (b) Nano drug-delivery systems use carriers such as liposomes and nanoparticles; they are not membrane bioreactors.

Remember · Membrane bioreactor = activated-sludge (microbial) treatment + membrane micro/ultrafiltration; compact, high-quality effluent fit for reuse. Used for sewage and industrial wastewater.

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Answer: (d) Power plants using fossil fuels

The US Environmental Protection Agency names the burning of fossil fuels by power plants and other industrial facilities as the largest source of sulphur dioxide in the air. Metal extraction, volcanoes, locomotives and ships are only smaller sources.

• ✓ (d) Power plants that burn fossil fuels are the largest source of SO2 in the atmosphere according to the EPA.
• ✗ (c) Extracting metal from ore is an industrial process the EPA lists among the smaller sources.
• ✗ (b) Ships, like locomotives (option a), burn fuel with a high sulphur content, but the EPA counts them among the smaller sources.

Remember · Largest SO2 source: fossil-fuel burning by power plants and other industry. Smaller: extracting metal from ore, volcanoes, locomotives, ships.

Question and answer: UPSC's official GS Paper I (2024, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (c) Only three

Hydrofluorocarbons (HFCs) replaced ozone-depleting CFCs and HCFCs in cooling, aerosol propellants, foam blowing and fire suppression. Lubricants are not an HFC application, so three of the four are correct.

• ✓ 1. HFCs serve as propellants in aerosol cans, one of the uses listed by the US EPA and UNEP.
• ✓ 2. HFCs are used as blowing agents to make insulating and other foams.
• ✓ 3. Some HFCs are used as fire-suppression (fire-extinguishing) agents, a replacement for ozone-depleting halons.
• ✗ 4. Lubricants are oils and greases; HFCs are gases used as refrigerants, propellants, blowing agents and fire suppressants, not as lubricants.

Remember · HFCs: refrigerants, AC, aerosols, foam blowing, fire suppression, solvents. Not ozone-depleting but potent greenhouse gases; phased down under the Kigali Amendment (2016).

Question and answer: UPSC's official GS Paper I (2023, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (b) Only two

Statements 1 and 2 are counted as correct, and statement 3 is wrong. A biofilter is the waste-treatment unit of a recirculating fish farm: its bacteria turn toxic ammonia from fish waste and feed into less harmful nitrate, and it does not add phosphorus.

• ✓ 1. Waste treatment in a recirculating system includes removing waste solids, both faeces and uneaten feed, and the biofilter is part of that treatment train. Strictly, the mechanical filter removes solids and the biofilter handles dissolved nitrogen; UPSC's key counts this statement as correct.
• ✓ 2. Nitrifying bacteria in the biofilter convert ammonia into nitrite and finally into nitrate, which is far less toxic to fish than ammonia.
• ✗ 3. The biofilter removes toxic ammonia; it does not add phosphorus. Phosphate is an inert dissolved compound that simply passes through the filtration stage.

Remember · In a recirculating aquaculture system, the biofilter's nitrifying bacteria convert toxic ammonia to nitrite and then to less toxic nitrate. It adds no phosphorus.

Question and answer: UPSC's official GS Paper I (2023, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (b) Only two

Statements 1 and 2 are correct; statement 3 is not. Gold mining and coal-fired power stations are both major sources of mercury releases, but international health bodies have set tolerable intake levels for mercury, so it is wrong to say that no safe level is known.

• ✓ 1. WHO lists mining for mercury, gold and other metals among the main human causes of mercury release, and warns that mercury use in artisanal and small-scale gold mining is particularly hazardous.
• ✓ 2. WHO names coal-fired power stations among the main sources of mercury releases. Coal contains mercury, which escapes when it is burned.
• ✗ 3. The FAO/WHO expert committee JECFA set a tolerable intake of 1.6 micrograms per kg of body weight per week for methylmercury. Exposure is harmful at high levels, but a tolerable level has been defined.

Remember · Mercury comes from coal burning and gold mining, among other sources. WHO and FAO experts have set a tolerable weekly intake for methylmercury, so a safe level is defined.

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Answer: (d) None

None of the statements is correct, because each says that no coal plant in India does something that at least one plant does. The private Mundra plant in Gujarat uses seawater, and many coal plants stand in water-stressed areas.

• ✗ 1. The 4,000 MW Mundra Ultra Mega Power Project, a coastal plant, uses seawater; the Central Electricity Authority lists its water source as seawater, with fresh water made by desalination.
• ✗ 2. A World Resources Institute study, cited in a NITI Aayog-hosted report, found that more than 70% of India's coal power plants are in water-stressed or water-scarce areas.
• ✗ 3. Mundra UMPP is developed and run by Coastal Gujarat Power Limited, a Tata Power company, so privately owned coal plants exist. Coal capacity is spread across central, state and private owners.

Remember · A single counter-example defeats an 'none of them' claim: Mundra (Tata Power) is a private coal plant using seawater, and most coal plants lie in water-stressed areas.

Question and answer: UPSC's official GS Paper I (2023, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (c) All three

All three activities are discussed as ways to capture and lock away carbon dioxide. Spreading crushed basalt (enhanced weathering) and adding lime to the sea (ocean alkalinity enhancement) are carbon-removal options assessed by the IPCC, and abandoned mines are listed among niche sites for underground CO2 storage.

• ✓ 1. Enhanced weathering spreads crushed silicate rock such as basalt on soil so that it reacts with atmospheric CO2. The IPCC cites estimates that spreading basalt on farmland in 12 countries could remove up to 2 GtCO2 a year by 2050.
• ✓ 2. Ocean alkalinity enhancement adds alkaline material such as lime to the sea so that it takes up and stores more CO2. The IPCC notes this idea goes back to a 1995 proposal to dissolve highly reactive lime in surface ocean water.
• ✓ 3. The IPCC's report on CO2 capture and storage names abandoned mines, along with basalts and salt caverns, as niche options for geological storage of captured CO2.

Remember · Enhanced weathering (crushed basalt on land), ocean alkalinity enhancement (lime in the sea) and storing captured CO2 underground, even in abandoned mines, are all discussed for carbon removal.

Question and answer: UPSC's official GS Paper I (2023, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (b) 1 and 4 only

Statements 1 and 4 are correct. WHO's 2021 guidelines set PM2.5 at 5 µg/m3 a year and 15 µg/m3 over 24 hours, and ozone can trigger asthma. Ozone peaks in hot, sunny weather, not bad weather, and it is PM2.5, not PM10, that WHO says can enter the bloodstream.

• ✓ 1. The WHO Air Quality Guidelines (2021) recommend an annual average of 5 µg/m3 and a 24-hour average of 15 µg/m3 for PM2.5.
• ✗ 2. Ground-level ozone forms when pollutants react in sunlight, so it is most likely to reach unhealthy levels on hot sunny days, not in inclement weather.
• ✗ 3. Both PM2.5 and PM10 can go deep into the lungs, but WHO says only the finer PM2.5 can even enter the bloodstream.
• ✓ 4. Ozone irritates and inflames the airways, aggravates asthma and increases the frequency of asthma attacks.

Remember · WHO 2021: PM2.5 annual 5, 24-hour 15 µg/m3 (PM10: 15 and 45). Ozone peaks on hot sunny days and worsens asthma. Only PM2.5 reaches the blood.

Question and answer: UPSC's official GS Paper I (2022, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (a) 1 and 3

Statements 1 and 3 are correct: PET is the polyester of clothing, blended with cotton and wool, and PET bottles are recycled, mostly into polyester fibre. Statement 2 is wrong because PET lets in oxygen and is unsuited to long storage of some alcoholic drinks. Statement 4 is wrong because burning PET turns its carbon into carbon dioxide, a greenhouse gas.

• ✓ 1. PET fibres are used alone or blended with natural fibres such as cotton, and wool-polyester and cotton-polyester blends are common textile mixes.
• ✗ 2. PET has only moderate oxygen permeability, so it suits short storage but harms the aroma of an alcoholic drink such as wine when kept for long. It is not fit for any and every alcoholic beverage.
• ✓ 3. PET bottles are mechanically recycled; in India most recycled PET, about 95% by one estimate, is spun into polyester fibre.
• ✗ 4. Burning plastic releases CO2 in proportion to its carbon. EPA's model takes PET as 63% carbon, with about 98% of that carbon turning into CO2 on combustion.

Remember · PET = polyester: blended with cotton and wool, and recycled (mostly into fibre). Burning it releases CO2, and it is a poor container for long-stored alcoholic drinks.

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Answer: (d) 2 and 3

Statements 2 and 3 are correct. Statement 1 is wrong because nanoparticles (particles of about 100 nanometres or less) also form naturally, for example in volcanic plumes and by erosion, apart from those made by humans.

• ✗ 1. Nanoparticles form naturally: gas-phase reactions that make them occur in the atmosphere and in volcanic plumes, and erosion of clay and plant debris makes them in liquids. Human activities such as cooking and welding add more.
• ✓ 2. Metal-oxide nanoparticles such as nano titanium dioxide are put into sunscreens and other cosmetic products.
• ✓ 3. Engineered nanoparticles from consumer products are now a source of exposure, and some materials become toxic when inhaled as nanoparticles, causing lung inflammation and heart problems.

Remember · Nanoparticles (about 100 nm or less) occur naturally too. Nano titanium dioxide goes into sunscreens and cosmetics; some engineered nanoparticles are hazardous when inhaled.

Question and answer: UPSC's official GS Paper I (2022, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (b) 2 and 4 only

Nitrogen oxides and sulphur dioxide cause acid rain: in the air they turn into nitric and sulphuric acids that fall with rain. Carbon monoxide and ozone are pollutants too, but they do not form these acids.

• ✓ 2. Nitrogen oxides (NOx) react with water, oxygen and other chemicals in the air to form nitric acid.
• ✓ 4. Sulphur dioxide (SO2) reacts with water, oxygen and other chemicals in the air to form sulphuric acid.
• ✗ 1. Carbon monoxide is a poisonous gas from incomplete burning of fuel; it is not one of the gases that make acid rain.
• ✗ 3. Ozone near the ground harms lungs and plants but is not an acid-rain gas.

Remember · Acid rain = SO2 + NOx turning into sulphuric and nitric acids; rain with pH below 5.6 is called acid rain.

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Answer: (a) environmentally responsible practices in electronics recycling industry

R2 stands for 'Responsible Recycling', a certification standard for electronics recyclers. Recyclers audited against it show that they handle used electronics and e-waste safely for the environment, workers and data security.

• ✓ (a) The R2 (Responsible Recycling) Standard is one of two accredited certification standards the US Environmental Protection Agency recognises for electronics recyclers.
• ✗ (b) Ramsar sites are managed under the Ramsar Convention's own guidance, such as the Montreux Record; R2 has nothing to do with wetlands.
• ✗ (d) Environmental Impact Assessment is a separate regulatory process for projects, not the R2 recycling code.

Remember · R2 = Responsible Recycling, a voluntary certification for electronics (e-waste) recyclers; its main counterpart is the e-Stewards standard.

Question and answer: UPSC's official GS Paper I (2021, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (b) 2 and 3 only

Most copper comes from sulphide ores, so smelting them drives off sulphur dioxide, a major air pollutant. The glassy waste left behind, copper slag, still carries heavy metals that can contaminate soil and water if stored carelessly. Releasing lethal amounts of carbon monoxide is not the recognised hazard of these plants.

• ✗ 1. The air-pollution concern linked to smelting ores that contain sulphur is sulphur dioxide, not lethal quantities of carbon monoxide; UPSC's key treats statement 1 as wrong.
• ✓ 2. Copper slag (Ferro sand) contains arsenic, cadmium, chromium, cobalt, nickel, lead and zinc, and the CPCB guideline asks smelters to store slag on an impermeable base with a garland drain to prevent soil and groundwater contamination.
• ✓ 3. Roasting and smelting sulphide ores releases sulphur dioxide; the WHO lists the smelting of sulphur-bearing ores as a main source of SO2.

Remember · Copper smelters: sulphur dioxide (from sulphide ores) in the air, and heavy-metal leaching from slag heaps.

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Answer: (d) 1, 2 and 3

Furnace oil is a heavy residual fuel left after the lighter fractions are distilled from crude oil in a refinery. Industries burn it in boilers, furnaces and captive power plants, and because it is rich in sulphur, burning it releases sulphur dioxide. All three statements hold.

• ✓ 1. It is the heavy residue that remains after refineries distil off the lighter products, which is why it is also called residual fuel oil.
• ✓ 2. Heavy fuel oil is used to produce electric power and for many industrial heating purposes, including captive generation.
• ✓ 3. Burning oil that contains sulphur emits sulphur dioxide, and furnace oil is among the higher-sulphur fuels, so its use adds SO2 to the air.

Remember · Furnace oil = heavy residual refinery product; burnt in industrial boilers and power units; high sulphur, so a source of SO2.

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Answer: (b) 1, 2 and 4 only

Pollution-derived magnetite nanoparticles form when iron-bearing material is burnt or heated by friction, so they come from vehicle engine exhaust, brake wear and combustion at power stations. A 2016 study found such particles in human brain tissue and linked them to oxidative damage of the kind seen in Alzheimer's disease. Microwave ovens and telephone lines are not among the sources it names.

• ✓ 1. Frictional heating of brake pads produces high-temperature magnetite nanoparticles at the roadside.
• ✓ 2. Magnetite nanoparticles have been captured from the exhaust plume of diesel engines; combustion is the main source.
• ✗ 3. The study names open fires and poorly sealed cooking or heating stoves as indoor sources of magnetite nanoparticles; microwave ovens are not among them.
• ✓ 4. The study shows spherical, fused magnetite particles collected at a power station, an example of industrial combustion.
• ✗ 5. Telephone lines are not among the sources the study names; they carry electrical signals, not iron-oxide particles from combustion or friction.

Remember · Airborne magnetite nanoparticles come from combustion and friction: vehicle exhaust, brake wear, power plants, open fires. They have been found in human brain tissue.

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Answer: (b) Polycarbonate

BPA is the building-block chemical of polycarbonate, the hard, clear plastic used in reusable bottles and food containers. It is also used in epoxy resins, such as the lining of food cans. The official agencies name only these two plastics as its main uses, so the other options fail.

• ✓ (b) Polycarbonate is made by joining BPA units, so BPA is a structural part of it. Small amounts can leach into food or drink, which is why BPA is a health concern (it can act on the hormone system).
• ✗ (a) Low-density polyethylene (carry bags and films) is not among the plastics that US and EU agencies name as made with BPA; they name polycarbonate and epoxy resins.
• ✗ (c) PET, the plastic of soft-drink and water bottles, is not among the plastics that US and EU agencies name as made with BPA; polycarbonate is the BPA-based bottle plastic.
• ✗ (d) Polyvinyl chloride is not among the plastics that US and EU agencies name as made with BPA; they name polycarbonate and epoxy resins.

Remember · BPA goes into polycarbonate plastics and epoxy resins (can linings). It is a suspected hormone disruptor.

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Answer: (d) Toiletries

Triclosan is an antibacterial chemical added to personal-care products such as some soaps, skin cleansers, deodorants and toothpastes, which are toiletries. It is a suspected endocrine (hormone-system) disruptor, so long exposure to high levels is a worry.

• ✓ (d) The US FDA says triclosan is added to some antibacterial soaps and body washes, toothpastes and cosmetics, all toiletries. Some short-term animal studies link high doses to lower levels of some thyroid hormones, which is why long exposure is a concern.
• ✗ (a) Food preservatives keep food from spoiling; triclosan is not a permitted food preservative. It is an antibacterial for personal-care products.
• ✗ (b) Fruit-ripening substances are chemicals that release ethylene, the ripening hormone of plants. Triclosan is not a ripening agent.
• ✗ (c) Triclosan is mainly an antibacterial added to personal-care products. The usual worry about reused plastic containers is a different one: chemicals such as BPA leaching out of the plastic.

Remember · Triclosan is an antibacterial agent in toiletries (soaps, toothpaste, deodorants) and a suspected endocrine disruptor.

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Answer: (a) 1, 2 and 3 only

Benzene is a volatile chemical released when fuels and other organic material burn, so vehicle exhaust, tobacco smoke and wood burning are all recognised sources of exposure. Varnished wooden furniture and polyurethane products are not named in the official lists of benzene sources.

• ✓ 1. Benzene is present in motor vehicle exhaust and in petrol (gasoline) vapour.
• ✓ 2. Tobacco smoke contains benzene, and WHO calls active and passive smoke exposure a significant source of exposure.
• ✓ 3. Wood-burning fires are named among the common sources of benzene in air.
• ✗ 4. UPSC's key does not count this as a benzene source. EPA's summary names glues, paints and furniture wax among household sources, but not varnished wooden furniture itself.
• ✗ 5. Polyurethane products are not named among the recognised benzene sources in the EPA and WHO summaries, and UPSC's key does not count them.

Remember · Benzene comes from burning and fuels: vehicle exhaust, tobacco smoke, wood-burning fires, petrol vapour, and some glues and paints.

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Answer: (d) 1, 2 and 3

Steel slag, the solid waste left when steel is made, is usable in all three ways: as stone-like aggregate in road layers, as a soil conditioner in farming, and as an ingredient in cement.

• ✓ 1. Processed steel slag replaces natural stone aggregate in roads; CSIR-CRRI has framed guidelines for using it in various road works, and a six-lane highway near Surat was built with it.
• ✓ 2. The Ministry of Steel lists agriculture as a use, where the slag stands in for soil nutrients and fertilisers, and its website mentions soil conditioning.
• ✓ 3. The Ministry of Steel names 'green cement' among the uses of steel slag; note that blast-furnace (iron) slag is the type mostly used in cement making today.

Remember · Steel slag is a waste-to-wealth material: road aggregate, soil conditioner, cement ingredient and rail ballast.

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Answer: (d) 1, 2 and 3

All three statements are correct: coal ash carries toxic trace metals such as arsenic, lead and mercury, coal-burning power plants emit sulphur dioxide and nitrogen oxides, and Indian coal is high in ash.

• ✓ 1. Coal and its fly ash hold toxic trace elements; the US Geological Survey names arsenic, selenium, lead and mercury among those tested in fly ash.
• ✓ 2. CPCB's standards for coal-based thermal power plants set limits for sulphur dioxide and oxides of nitrogen in the flue gas, because burning coal releases both.
• ✓ 3. The Ministry of Coal states that coal produced in India generally has 25 to 45 per cent ash, against 10 to 20 per cent for imported coal, which is why washing of coal is promoted.

Remember · Coal power means SO2 and NOx in the air and ash laden with arsenic, lead and mercury on the ground; Indian coal is high in ash.

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Answer: (d) Waste-to-energy technologies

Pyrolysis and plasma gasification are waste-to-energy technologies: they treat waste (such as plastics and municipal solid waste) at high temperature and turn it into fuel oil or syngas that can generate power.

• ✓ (d) In pyrolysis, waste is heated (400-600°C) without oxygen to give pyrolysis oil and gas. In plasma gasification, a plasma arc above 3000°C turns waste into syngas, which can run gas engines to make electricity.
• ✗ (a) Rare earth elements are recovered from ores by mining and chemical processing, not by these thermal waste treatments.
• ✗ (b) Natural gas extraction uses drilling and hydraulic fracturing; neither term belongs there.
• ✗ (c) Hydrogen vehicles run on fuel cells or hydrogen engines; pyrolysis and gasification are not vehicle technologies.

Remember · Pyrolysis (heating waste without oxygen) and plasma gasification (waste to syngas in a plasma arc above 3000°C) are waste-to-energy routes for plastics and solid waste.

Question and answer: UPSC's official GS Paper I (2019, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (a) They are considered harmful to marine ecosystems.

Microbeads are tiny plastic beads put into cleansers and toothpastes as exfoliants; they slip through water filters, end up in oceans and lakes, and threaten aquatic life.

• ✓ (a) Microbeads are a type of microplastic. They pass easily through water treatment systems into the sea, where marine animals can swallow them and toxins can collect on them, so they are a threat to marine ecosystems.
• ✗ (b) Microbeads are rinsed off the skin and the worry about them is environmental pollution; skin cancer in children is not the reason for the concern.
• ✗ (c) Plastic beads are not taken up into crop plants through their roots; this is not the reason for concern.
• ✗ (d) Microbeads are used in personal care products, not as food additives or adulterants.

Remember · Microbeads are tiny plastic exfoliant beads in cosmetics and toothpaste that escape water treatment and pollute oceans, harming aquatic life.

Question and answer: UPSC's official GS Paper I (2019, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (d) 1, 2, 3 and 4

Why not the tempting option · UPSC's key counts ozone among the gases released due to crop-residue burning. Ozone is a secondary pollutant that forms in the air from the nitrogen oxides and volatile organic compounds in the smoke, but the question says 'due to the burning', which covers that. The doubt does not change the answer: carbon monoxide, methane and sulphur dioxide are certainly emitted, and (d) is the only option that contains all three. In the exam, settle the sure statements first and let the option grid decide the rest.

UPSC counts all four. Burning crop residue puts carbon monoxide, methane and sulphur dioxide straight into the air, and the smoke's nitrogen oxides and volatile organic compounds go on to form ground-level ozone. Since 1, 2 and 4 are certain, only option (d) can be right.

• ✓ 1. Burning rice straw releases carbon monoxide; about 7% of the carbon in the straw leaves as CO.
• ✓ 2. Methane is also released; about 0.66% of the carbon in burnt rice straw is emitted as CH4.
• ✓ 3. Ozone is not emitted as such; it forms in the air from the nitrogen oxides and volatile organic compounds in stubble smoke, so it is released into the atmosphere 'due to' the burning. In any case CO, CH4 and SO2 are certain, and (d) is the only option that contains all three.
• ✓ 4. Stubble burning emits sulphur dioxide along with carbon monoxide, nitrogen oxides, methane and fine particles.

Remember · Crop-residue burning gives CO, CO2, CH4, N2O, NOx, SO2 and particulates; the smoke's VOCs and NOx then form ground-level ozone.

Question and answer: UPSC's official GS Paper I (2019, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 1 Oct 2026 (how we verify). Permalink · Report an error

Answer: (a) pesticides in agriculture

Carbofuran, methyl parathion, phorate and triazophos are toxic insecticides used on crops. They feature in the Government of India's lists of pesticides that are banned or restricted because of their harm to health and to birds, fish and bees.

• ✓ (a) All four names appear in the Ministry of Agriculture's list of banned and restricted pesticides. Methyl parathion was banned by an August 2018 order, and phorate and triazophos were barred from manufacture and import from 1 January 2019, with use to end by 31 December 2020.
• ✗ (b) Food preservatives are additives regulated under food-safety rules; none of these four is a preservative.
• ✗ (c) Fruit ripening is done with ethylene-releasing agents or, illegally, calcium carbide. These chemicals are insecticides, not ripening agents.
• ✗ (d) Moisturisers in cosmetics are humectants and emollients; these four are toxic to humans and have no cosmetic use.
• • Since then The Government's list of pesticides banned for manufacture, import and use, updated to 1 October 2022, includes methyl parathion, phorate and triazophos; carbofuran appears as a banned 50% SP formulation.

Remember · Carbofuran, methyl parathion, phorate and triazophos are hazardous agricultural insecticides, banned or being phased out in India.

Question and answer: UPSC's official GS Paper I (2019, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error