Which of the following energy sources produces no atmospheric pollution?

Solar energy is the answer. Photovoltaic and solar thermal systems convert sunlight directly into electricity or heat without burning anything, so they release no smoke, CO2, SO2 or particulates while running. Their environmental footprint lies in manufacturing panels and land use, not in generation.

Why the others fail:

• Petroleum is burnt in engines and refineries, releasing CO2, NOx, SO2 and particulate matter.
• Coal is the largest source of SO2 and fly ash from India's thermal power stations, and a major CO2 emitter.
• Nuclear is nearly free of air pollutants during operation, which is why it is called low-carbon. The question's intended answer is solar because it is clean on every count, whereas nuclear leaves radioactive waste that needs long-term management. Keep that distinction clear.

Concept: the pollution profile of different energy sources, linked to India's renewable targets under the National Action Plan on Climate Change and the Paris commitments. In Mains, this feeds into GS-3 on energy security and climate change.

Trap: choosing nuclear because it is described as zero-emission. Pollution is not the same as waste, and this question is about the atmosphere, where solar is cleanest.