(a) Minerals containing iron are called ferrous minerals, e.g., iron ore and manganese. Minerals which do not contain iron are called non-ferrous minerals, e.g., bauxite, lead and gold.
(b) Conventional sources of energy are generally exhaustible and polluting, e.g., firewood, coal and petroleum. Non – conventional sources of energy are usually inexhaustible and non-polluting, e.g., solar, wind, tidal and atomic energy.

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