Which one among the following substances does not contribute to global warming?

The correct answer is A. Oxides of sulphur and nitrogen are the option that does not add to warming, at least in the net sense the question intends.

• Carbon dioxide (C): the main long-lived greenhouse gas from fossil fuel burning and deforestation, so it contributes to warming.
• Methane (B): a potent greenhouse gas, about 80 times more warming per unit mass than CO2 over 20 years, from wetlands, paddy fields, livestock and landfills.
• Water vapour (D): the most abundant greenhouse gas in the atmosphere. It acts as a feedback, since warmer air holds more moisture.
• Oxides of sulphur and nitrogen (A): sulphur dioxide forms sulphate aerosols that reflect sunlight and produce a cooling effect. Nitrogen oxides are more complicated, since N2O is a greenhouse gas and NOx helps form ozone, but the sulphur-based cooling is why this option is treated as non-contributing.

The core concept is the difference between greenhouse gases that trap outgoing infrared radiation and aerosols that reflect incoming sunlight. This links to Environment and Climate Change, and to Mains questions on climate feedbacks and the trade-off in clean-air policy.

Trap: assuming every pollutant gas warms the planet. Aerosol-forming gases can do the opposite.