Flyash pollution is caused by

1. A

   Oil refining

   Oil refining yields gases, liquid hydrocarbons and sludge; fly ash is not its characteristic solid waste.

2. B

   Fertilizer industry

   Fertiliser plants may emit fluoride, ammonia or gypsum-related wastes. Fly ash is not their signature pollutant in this item.

3. C

   Thermal power plant

   Fly ash is the fine residue of pulverised coal burnt in thermal power stations. That industry is the official key.

4. D

   Mining

   Mining produces overburden, tailings and dust, not the siliceous fly ash of coal boilers.

Summary. Official key is (c) thermal power plant. Indian coal is high-ash; electrostatic precipitators and ash ponds are the usual controls; fly ash is also pushed into cement and bricks. Refineries, fertiliser units and mines have other waste streams. Honour the stored letter (c).