SSC CGL 2024 Tier-I · 17 September 2024, Shift 3 · General Awareness · Question 16 of 98

Text as printed on a candidate's response sheet for this shift; answer per SSC's tentative key as marked on that sheet. Solution last reviewed 6 September 2026.

Where this paper and its answers come from

SSC does not publish CGL question papers or a public answer key. The questions and options here are reproduced as printed on a candidate's own response sheet for this shift — the Commission's text, unchanged. Each answer is SSC's tentative key as marked on that sheet; SSC allowed challenges to it and never publishes a final key. The solutions are written by UnlockIAS.

Which of the following is NOT a greenhouse gas?

(a)Nitrous oxide
(b)Methane
(c)Carbon dioxide
(d)Nitric oxide

Answer

Why

Correct — D. Nitric oxide (NO) is an air pollutant, not a greenhouse gas. It is one of the NOx gases produced by combustion, it survives in the air for days rather than decades, and its effect on climate is indirect, through smog and ozone chemistry.

Carbon dioxide, methane and nitrous oxide are all counted greenhouse gases, which leaves nitric oxide, option (d), as the odd one out.

The trap is the near-identical name: nitrous oxide (N2O) is a greenhouse gas, nitric oxide (NO) is not.

Why the others are wrong

(a)
Nitrous oxide — Nitrous oxide (N2O) is a greenhouse gas, long-lived in the atmosphere and released mainly from nitrogen fertiliser and manure. It sits in the Kyoto basket with CO2 and methane.
(b)
Methane — Methane (CH4) traps far more heat per molecule than CO2 over a short horizon and comes from paddy fields, livestock, landfills and fossil-fuel leaks. It is a greenhouse gas on every listing.
(c)
Carbon dioxide — Carbon dioxide is the reference greenhouse gas — every other gas has its warming potential quoted relative to it — so it cannot answer a question asking which gas is NOT one.

Concept

A greenhouse gas absorbs infrared radiation leaving the Earth and re-emits it, warming the lower atmosphere. The main ones are carbon dioxide, methane, nitrous oxide, water vapour, ozone and the industrial fluorinated gases.

NOx — nitric oxide and nitrogen dioxide — is a different family altogether. These are reactive pollutants from vehicle engines and power plants, and what they cause is acid rain and photochemical smog.

The question works precisely because one nitrogen oxide belongs to the first list and another to the second.

Nitric oxide is not climate-inert in a laboratory sense, but it is present in traces and gone within days, so no climate accounting framework lists it as a greenhouse gas. That is the sense in which the question is asked.

Key facts

Nitrous oxide (N2O) is a greenhouse gas, while nitric oxide (NO) is classed as a NOx air pollutant.
The Kyoto Protocol basket covers carbon dioxide, methane, nitrous oxide, HFCs, PFCs and sulphur hexafluoride, with nitrogen trifluoride added by the Doha Amendment.
NOx gases drive photochemical smog and acid rain rather than long-term warming.

Study next

The Kyoto Protocol basket and global warming potentialPhotochemical smog and the role of NOxOzone depletion and global warming as two distinct problems

Common traps

Reading 'nitric' and 'nitrous' as the same word under time pressure.
Assuming every polluting gas must also be a greenhouse gas.

SSC keeps atmosphere questions factual rather than analytical — the kind of radiation absorbed by the ozone layer is asked at 11 Sep 2024, 9:00 am, GA Q.20.

Related PYQs

No directly related past PYQ was found.