In a village people burn wood and cow dung as a fuel for basic necessity. In other nearby village, they have a big biogas plant in which biowaste is used to prepare biogas. If we compare the situation of both villages, I will prefer to have biogas plant as it cleans the surroundings of biowaste. It is environment friendly, no pollution, produces electricity and cooking gas and at last waste can be used as manure.

Petroleum is believed to be formed from organisms living in the sea. As these organisms died, their bodies settled at the bottom of the sea and got covered with layers of sand and clay. Over millions of years, the dead organisms were transformed into petroleum oil and natural gas and other fossil fuels under the conditions of the absence of air, high temperature and high pressure. Like coal, petroleum and natural gas are also fossil fuels.
Since oil and gas are lighter than water and do not mix with it, they move upward. They are stopped by the overlying rocks which they cannot break through.

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

Exhaustible natural resources are as below: Coal, natural gas, petroleum, minerals, forests. Inexhaustible natural resources are as below: Air, sunlight, oxygen.

Millions of years ago, the earth had dense forests in low lying wetland areas. Due to natural processes like flooding and earthquakes, these forests got buried under the soil. As more soil deposited over them, they were compressed. The temperature also rose as they sunk deeper and deeper. Under high pressure and high temperature, dead plants got slowly converted into coal. The process of conversion of dead vegetation into coal is called carbonisation.

CNG: Compressed Natural Gas.
LPG: Liquefied Petroleum Gas.

In India, coal is found mainly in Bihar, West Bengal, Orissa and Madhya Pradesh.

It was drilled in Makum in Assam.

The known reserves of these will last only a few hundred years is true, as we know that coal and petroleum are fossil fuels. It requires the dead organisms millions of years to get converted into these fuels. Excessive and injudicious use of these fuels leads to shortage of these fuels and their use is also linked to global warming. It is therefore necessary that we use these fuels only when absolutely necessary.

1. Fossil Fuels
2. Refining
3. Coke
4. Petrol
5. Coal
6. Diesel
7. Bitumen
8. Petroleum

(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.

(a) Coal.
(b) It is solid and black coloured.
(c) Y is carbonisation and Z is destructive distillation.
(d) A is coke, B is coal gas while C is coal tar.

When coal is strongly heated in the absence of air in closed retorts, various useful products are obtained. These are coke, coaltar and coal gas.
Uses of coke Coke is used in the manufacture of steel and in the extraction of many metals. It acts as a fuel and it is a better fuel than coal.
Uses of coal tar The various compounds obtained from coal tar are used as starting materials for manufacturing a large number of substances used in everyday life and in industry like synthetic dyes, drugs, explosives, perfumes, plastics, paints, photographic materials, roofing materials, etc. Naphthalene balls used to repel moths and other insects are also obtained from coaltar.
Uses of coal gas It is used as a fuel in many industries situated near the coal processing plants.