(a) What is the difference between a thermal power plant and a hydro power plant?
(b) Which of the two causes serious air pollution and how?

(a) The difference between a thermal power plant and a hydro power plant is:

Thermal power plant	Hydro power plant
1. A thermal power plant uses non-renewable sources of energy like coal, oil or gas to drive turbines.	1. A hydro power plant uses a renewable source of energy, water to rotate turbines.
2. A thermal power plant causes air pollution due to the burning of fossil fuels.	2. A hydropower plant is environment friendly.

(b) A thermal power plant causes serious air pollution because it emits harmful gases and fly-ash into the air, due to the burning of fossil fuels in large amounts everyday.