Which of the following group of gases contribute to the “Green House Effect”?

The correct answer is D, Carbon dioxide and Methane. These are the two principal greenhouse gases in the atmosphere. CO2 is the largest contributor to radiative forcing since the Industrial Revolution, and methane is a far more potent gas per molecule, with a 100-year global warming potential of roughly 28 times that of CO2 under the IPCC AR5 values.

The core concept is that these gases absorb outgoing infrared radiation from the Earth's surface and re-emit it, which warms the lower atmosphere. This is the natural greenhouse effect, which becomes enhanced when human activity raises concentrations. For Mains, link this to climate change, fossil fuel emissions, and the Paris Agreement.

• A: Ammonia is not a significant greenhouse gas. Ozone is, but only as a tropospheric pollutant, so the pair fails.
• B: Carbon monoxide is only an indirect greenhouse agent. Sulphur dioxide mainly has a cooling effect through sulphate aerosols.
• C: Nitrous oxide and CF4 are both Kyoto-basket gases, so the pair is technically defensible. It is a weaker choice than D, which names the two dominant gases the examiners intended.

Trap: Candidates often pick A because ozone is a greenhouse gas, forgetting that ammonia is not one of the standard GHGs. Another trap is treating SO2 as a warming gas.