About 300 million years ago, the earth had dense forests in low lying wetland areas. Due to natural processes like flooding, these forests got buried under the soil and deposited as fossil. Due to high temperature and pressure, dead plants got slowly converted into coal.

Decantation can be used to separate a mixture of petroleum and water. The mixture is allowed to stand. Carefully, lighter layer can be poured and separated without disturbing the heavier one.

Disadvantages of using fossil fuels are
(i) It causes air pollution.
(ii) It causes global warming because they produce greenhouse gas, i.e. carbon dioxide on burning
(iii) The by-products of burning fuels cause acid rain which pollute water resources

Difference between coke and coal are as follows:

The advantages of using CNG and LPG as fuels are as follows :
(i) CNG and LPG are clean fuels.
(ii) They do not produce pollution.
(iii) They are easily available.
(iv) They can be used directly for burning.
(v) They are easy to transport.
(vi) Their cost is low.

CNG is a good alternative to petrol and diesel in vehicles because it is a clean fuel and does not cause air pollution. It is filled in cylinders.

Diesel is used to run electric generators.

Petroleum is called black gold due to its great commercial importance.

Gaseous fuels are preferred because they burn completely liberating large amount of heat leaving behind no ash.

Coke

(a) A is petroleum and B is natural gas.
(b) A is thick liquid while B is gas.
(c) C is called fractional distillation
(d) D is kerosene.

The natural resources which are present in a limited quantity in nature and can be exhausted (used up) by human activities are called exhaustible natural resources, e.g. coal, petroleum, natural gas, minerals, forests, wildlife, etc.
It requires millions of years for the conversion of the dead organisms into petroleum, from which petrol is separated. So, once the present stock of it gets exhausted, no new supplies of it will be available to us in the near future, whereas sunlight is present in an unlimited quantity in nature, so it is inexhaustible natural resource. It is not likely to be exhausted by human activities.