When the powder of a common metal is heated in an open china dish, colour turns black. However, when hydrogen gas is passed over the hot black substance formed, it regains its original colour. Based on this information, answer the following questions :
(i) What type of chemical reaction takes place in each of the two given steps ?
(ii) Name the metal initially taken in the powder form. Write balanced chemical equations for both these reactions.

Explanation

(i) The available information suggests the metal is copper. In open air, its is oxidised to form copper (II) oxide which is black in colour. The reaction is known as oxidation reaction. On passing hydrogen gas over the hot substance, the original colour of the metal is regained. It is an example of reduction reaction.
(ii) The balanced chemical equations for the reactions are :
`underset(("Metal"))(2Cu(s)) + O_(2)(g) overset("heat")rarr underset(("Black"))underset("Copper (II) oxide")(2CuO(s))`
`CuO(s) + H_(2)(g) overset("heat")rarrCu(s) + H_(2)O(g)`