Explain the following :
(i) `Cu^(+)` is colourless and `Cu^(2+)` is coloured.
(ii) Zn shows only +2 oxidation state it its compounds.

Explanation

(i) `Cu^(+)` has `3d^(10)` configuration ( no d-d transition of electrons ) while `Cu^(2+)` ion has `3d^(9)` configuration (d-d transition is possible ). As a result, `Cu^(2+)` is colourless and `Cu^(2+)` is coloured.
(ii) The configuration of Zn is `[Ar]3d^(10)4s^(2)`. By losing two electrons, `Zn^(2+)` ion has `[Ar]3d^(10)` configuration whihc is symmetrical . `Zn^(2+)` ion has no tendency to lose any more electrons. Therefore, Zn shows only +2 oxidation state in its compounds.