Previous Year Question

Nitrogen (N2) is not a greenhouse gas. Although nitrogen and oxygen constitute most of Earth's atmosphere, they do not absorb the infrared radiation emitted by the Earth in the way greenhouse gases do. NASA explains that the major atmospheric gases nitrogen and oxygen do not absorb infrared radiation, whereas gases such as carbon dioxide, water vapour and methane do.

Among the other three options, methane (CH4), carbon dioxide (CO2), and chlorofluorocarbons (CFCs) all contribute to the greenhouse effect. NASA officially includes water vapour, CO2, methane, nitrous oxide and chlorofluorocarbons among greenhouse gases.

An important point is that nitrogen constitutes about 78% of the atmosphere but is not a major greenhouse gas, whereas gases such as CO2 and CH4 can influence Earth's heat balance even at much lower concentrations because they interact effectively with infrared radiation. Thus, greenhouse behaviour depends not simply on atmospheric abundance but on a molecule's ability to absorb infrared radiation.