(a) List any two

(a) Characteristics of a good fuel:

(i) It should have a high calorific value.

(ii) It should burn without giving out any smoke or harmful gases. (iii) Its ignition temperature should neither be too low nor too high. (iv) After burning it should not leave much ash behind. (any two)

(b) Those sources of energy which have accumulated in nature over a very-very long time and cannot be quickly replaced when exhausted, are called non-renewable sources of energy. Example: Fossil fuels (coal, petroleum, natural gas) and nuclear fuels (uranium) are non-renewable sources of energy.