`Zn^(2+)` salts are white while `Cu^(2+)` salts are blue, explain why ?

Explanation

Zn (II) and Cu (II) has electronic configurations as given below: Zn (II) : `[Ar]3d^10 4s^0` and `Cu (II): [Ar]3d^9 4s^0` .There is no unpaired electron in d-sub shell of Zn (II). Hence, it is white. On the other hand Cu (II) has one unpaired electron. Hence, it is coloured.