What is meant by fossil fuel?

(a) What is meant by fossil fuel ?
(b) Which fossil fuel is usually conserved when we save on electricity?
© At the present rate of consumption how long will the known reserves of coal and petroleum last ?

(a) Fossil fuels are non-renewable resources of energy which are formed from degradation of biomass of plants and animals buried deep under the earth million of years ago.
(b) Coal.
© Reserves of coal will last for 200 years, and reserves of petrol will last for 40 years.