A good source of energy fulfils the following criteria:

(I)It produces a lot of heat per unit mass.

(II) It does a huge amount of work per unit mass.

(III) It is easily accessible.

(IV) It is easy to store and transport.

(V)It is economical.

(VI)It produces less amount of smoke.

A good fuel produces a huge amount of heat on burning, does not produce a lot of smoke, and is easily available.

Natural gas can be used for heating and cooking food because it is a clean source of energy. It does not produce huge amount of smoke on burning. Although it is highly inflammable, it is easy to use, transport, and it produces a huge amount of heat on burning.

The disadvantages of fossil fuels are:
→ Burning of coal and petroleum produces a lot of pollutants causing air pollution.
→ Fossil fuels release oxides of carbon, nitrogen, sulphur, etc. that cause acid rain, which affects the soil fertility and potable water.
→ Burning of fossil fuels produce gases such as carbon dioxide that causes global warming.

Fossil fuels which are traditionally used by human beings everywhere as an energy sources are non-renewable sources of energy. These sources of energy are limited and will disappear after some time. They are being consumed at a large rate. Therefore, we should conserve the energy sources. Hence, we should look for alternate sources of energy.