Match the pollutants given in List – I with their effects given in List – II.
List – I
Pollutants
a. Phosphate fertilizers in water
b. Methane in air
c. Synthetic detergents in water
d. Nitrogen oxide

Question

Match the pollutants given in List – I with their effects given in List – II.
List – I
Pollutants
a. Phosphate fertilizers in water
b. Methane in air
c. Synthetic detergents in water
d. Nitrogen oxides in air
List – II
Effects of Pollutants
i. Biochemical oxygen demand level increase
ii. Acid Rain
iii. Global warming
iv. Eutrophication

UnlockIAS · Accepted Answer

Correct — option (2), 'a – iv, b – iii, c – i, d – ii,' matches each pollutant to the effect it is actually known for in environmental science. Phosphate fertilisers in water (a) cause eutrophication (iv): phosphate run-off from farmland is a limiting nutrient for aquatic plants and algae, so its excess triggers explosive algal growth, and when that algal bloom later dies and decomposes, the decomposition consumes dissolved oxygen and can leave a water body effectively dead. Methane in air (b) causes global warming (iii): methane is a potent greenhouse gas — molecule for molecule, far more effective at trapping heat than carbon dioxide over a 20-year horizon — released from sources such as wetlands, rice paddies, livestock digestion and landfills, and it is one of the principal non-CO2 drivers of anthropogenic climate change. Synthetic detergents in water (c) raise biochemical oxygen demand, BOD (i): detergents (and other organic pollutants) provide food for microorganisms in water, and as those microbes multiply to break the pollutant down, they consume dissolved oxygen, so a rising BOD is the standard laboratory measure of exactly this oxygen-depleting organic pollution load. Nitrogen oxides in air (d) cause acid rain (ii): NOx released mainly from vehicle exhaust and combustion reacts with atmospheric moisture to form nitric acid, which falls as acid precipitation alongside the sulphur-dioxide-derived sulphuric acid from the same combustion sources. Each of these four pollutant-effect pairs is a standard, independently verifiable fact of environmental chemistry, and the question simply asks a candidate to hold all four correctly in memory at once rather than confuse a pollutant with an effect it merely sounds similar to.

Why the other options are wrong — (a) Every pairing here is wrong. It assigns acid rain to phosphate fertilisers (that effect belongs to nitrogen oxides), rising BOD to methane (that effect belongs to synthetic detergents), eutrophication to synthetic detergents (that effect belongs to phosphate fertilisers), and global warming to nitrogen oxides (that effect belongs to methane). It is best read as a scrambled reassignment of the correct set rather than a partially right answer.  (c) This option also scrambles all four pairings: it gives global warming to phosphate fertilisers (methane's actual effect), acid rain to methane (nitrogen oxides' actual effect), eutrophication to synthetic detergents (phosphate fertilisers' actual effect), and rising BOD to nitrogen oxides (synthetic detergents' actual effect). None of the four assignments survives a check against the underlying chemistry.  (d) This option gets methane-global warming (b-iii) right but the remaining three wrong: it assigns rising BOD to phosphate fertilisers (that is synthetic detergents' effect), acid rain to synthetic detergents (that is nitrogen oxides' effect), and eutrophication to nitrogen oxides (that is phosphate fertilisers' effect). Getting one of four pairings correct is exactly what makes this option a believable distractor for a candidate who is sure about methane but has not fixed the other three.

Concept: Four classic pollutant-effect pairs recur across environmental-science questions: nutrient pollutants such as phosphates trigger eutrophication (excess algal growth followed by oxygen-depleting decomposition); organic pollutants such as synthetic detergents raise Biochemical Oxygen Demand, the measured oxygen microbes consume while breaking the pollutant down; potent greenhouse gases such as methane drive global warming; and combustion-derived gases such as nitrogen oxides (alongside sulphur oxides) form acid rain. Distinguishing these requires separating 'what the pollutant does directly' (adds a nutrient, adds an oxidisable organic load, traps heat, or forms an acid) from the downstream ecological consequence each mechanism produces.

State PCS 2025 Q31 — Environment & Ecology PYQ with Answer

State PCS 2025 Q31 — Environment & Ecology PYQ with Answer