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.

PCRA is the petroleum conservation research association. They advise people how to save petrol/ diesel while driving. Their tips are:
(i) Drive at a constant and moderate speed.
(ii) Switch off the engine at traffic lights, or at places where you have to wait.
(iii) Ensure correct tyre of pressure.
(iv) Ensure regular maintenance of the vehicle.

(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.

Fossil fuels will last only for a few hundred years because they are exhaustible natural resources. If consumed at a rate faster than the rate at which these are formed in nature, they will get exhausted very soon.
Once the present stock of these gets exhausted, no new supplies of these fossil fuels will be available to us in the near future because it required millions of years for the conversion of dead organisms into these fuels.

Burning of fuels is a major cause of global warming because they produce a lot of greenhouse gas 'carbon dioxide' on burning.
The earth's atmosphere allows most of the sunlight that falls on it to pass through and heat the surface. But greenhouse gases such as carbon dioxide, methane, water vapours trap the heat radiated from earth. This leads to an increase in earth's temperature. This is known as greenhouse effect.
When concentration of greenhouse gases such as carbon dioxide increases, greenhouse effect also increases. This is known as global warming. It may cause melting of ice caps and glaciers resulting the rise in sea levels.

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.

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.