Pollution MCQs for UPSC Prelims

Correct answer: B - 1 and 3 only

Statements 1 and 3 are the accepted sources, so (b) is correct. Smelting units release lead fumes and dust while extracting metals from ore, and lead-based pigments in paints remain a major exposure route, especially when old painted surfaces flake or are sanded. Statement 2 is wrong because pencil 'lead' is graphite mixed with clay and contains no metallic lead, and ordinary pens are not a lead hazard. Statement 4 is wrong as a general proposition: mainstream hair oils and cosmetics are not recognised lead sources, although adulterated traditional cosmetics like surma or kohl can contain lead, which is why a few keys debated this statement. The consensus key retains 1 and 3 only.

Correct answer: D - nitrous oxide and sulphur dioxide

Acid rain results when oxides of nitrogen and sulphur dioxide, released largely by burning fossil fuels, react with atmospheric water vapour to form nitric and sulphuric acids, so option (d) is correct. Carbon dioxide forms only weak carbonic acid and is not the principal cause, ruling out options (a), (b) and (c). Nitrogen gas itself is inert, and ozone and carbon monoxide are not the chief acidifying agents.

Correct answer: C - II and III only

India's per capita carbon dioxide emissions are around 1.8 to 2 tonnes, far above 0.5 tonne, so statement I is wrong. India ranks second in the Asia-Pacific region after China in emissions from fuel combustion, validating statement II, and electricity and heat generation, dominated by coal, is the single largest source of its emissions, validating statement III. Hence only II and III are correct.

Correct answer: D - Toiletries

Triclosan is an antibacterial and antifungal agent added to personal-care and toiletry products such as soaps, toothpastes, deodorants and cosmetics, making toiletries the correct context, option (d). It is not used as a food preservative (a), as a fruit-ripening agent (b), or as a component of plastic containers (c). Concern over triclosan stems from possible hormonal effects and its contribution to antimicrobial resistance with prolonged exposure.

Correct answer: C - Pollution assay in aquatic ecosystems

Biological Oxygen Demand measures the amount of dissolved oxygen consumed by micro-organisms while decomposing organic matter in water, so a high BOD indicates heavy organic pollution; it is therefore a standard criterion for pollution assay in aquatic ecosystems. It has nothing to do with oxygen levels in blood, oxygen in forests, or oxygen at high altitudes, so those options are incorrect.

Correct answer: A - NO2, O3 and peroxyacetyl nitrate in the presence of sunlight

Photochemical smog forms when nitrogen oxides and volatile organic compounds react in the presence of strong sunlight to produce ground-level ozone (O3) and secondary pollutants like peroxyacetyl nitrate (PAN), so option (a), which includes NO2, O3, PAN and sunlight, is correct. Option (b) wrongly substitutes carbon monoxide and oxygen as the key reactants. Option (c) is incorrect because photochemical smog requires sunlight and warm conditions, not low temperature, and omits ozone and PAN. Option (d) is wrong because it specifies the evening, whereas photochemical smog peaks in bright daytime sunlight that drives the reactions.

Correct answer: C - Statement-I is correct but Statement-II is incorrect

Statement-I is correct: India is the largest user of groundwater in the world, withdrawing more than a quarter of the global total annually, as noted in the UN World Water Development Report 2022. Statement-II is incorrect: the bulk of India's groundwater is drawn for irrigation in agriculture (around 80-90% of withdrawals), not to meet drinking water and sanitation needs; so the heavy extraction is not driven by the drinking-water requirements of its population. Hence Statement-I is correct but Statement-II is wrong, giving option (c). Options (a) and (b) wrongly accept Statement-II, and (d) wrongly rejects the true Statement-I.

Correct answer: D - 1, 2 and 3

Coal ash does contain toxic trace elements including arsenic, lead and mercury, which is why fly ash disposal is an environmental concern, so statement 1 is correct. Burning coal releases sulphur dioxide and oxides of nitrogen, key precursors of acid rain and air pollution, so statement 2 is correct. Indian coal is well known for its high ash content, often above 30 to 40 percent, so statement 3 is correct. Hence all three statements are correct.