UPSC CSE Prelims

Correct Option: D Explanation: Biomass burning directly releases carbon monoxide, methane and sulphur dioxide, and produces ozone-forming precursor gases. The exam key counts ozone among atmospheric pollutants resulting from biomass burning. Statement / Pair Analysis: 1 (Correct): Incomplete biomass combustion generates carbon monoxide. 2 (Correct): Incomplete burning emits methane and other hydrocarbons. 3 (Correct): Ozone rises secondarily when nitrogen oxides and volatile organic compounds react in sunlight; it is not usually emitted directly. 4 (Correct): Sulphur in plant matter can oxidise to sulphur dioxide in burning. Option-wise Analysis: A (Incorrect): It omits true item 3 (Ozone rises secondarily when nitrogen oxides and volatile organic compounds react in sunlight; it…); omits true item 4 (Sulphur in plant matter can oxidise to sulphur dioxide in burning). B (Incorrect): It omits true item 1 (Incomplete biomass combustion generates carbon monoxide). C (Incorrect): It omits true item 2 (Incomplete burning emits methane and other hydrocarbons); omits true item 3 (Ozone rises secondarily when nitrogen oxides and volatile organic compounds react in sunlight; it…). D (Correct): Includes all and only the true statements/pairs. Review Note: Important nuance: tropospheric ozone is primarily a secondary pollutant formed from crop-burning emissions, not a direct smoke constituent.