Flyash pollution is caused by

The correct answer is C) Thermal power plant. Fly ash is the fine, glassy residue left when pulverised coal burns in a boiler. Electrostatic precipitators capture it before the flue gas leaves the stack, but a large share still ends up in ash ponds and the air, so coal-fired thermal plants are the main source.

• Oil refining is wrong. Its pollutants are sulphur compounds, VOCs, refinery effluents and petroleum coke, not fly ash.
• Fertilizer industry is wrong. Its characteristic wastes are phosphogypsum, ammonia emissions and effluent sludge.
• Mining is wrong. It produces overburden, tailings, mine dust and acid mine drainage, not fly ash.

The core concept is combustion-generated particulate waste and its management. For Mains, link this to India's coal dependence, the fly ash notifications under the MoEFCC, which mandate utilisation in cement, bricks and road construction, and the ecological risk from heavy metals leaching from ash ponds.

Trap: aspirants pick mining because it is a heavy polluter of land and air. Fly ash is specifically a combustion by-product, so ask where the fuel is burnt.