Question

In which of the following pairs are both the ions coloured in an aqueous solution?

(a) Ni⁺², Ti⁺³
(b) Ni⁺², Cu⁺
(c) Sc⁺³, CO⁺²
(d) Sc⁺³, Ti⁺³

Answer 1

(a) Ni⁺², Ti⁺³

Ni⁺² = [Ar] 3d⁸ t_2g⁶ e_g². It has 2 unpaired electron in e level. Hence it is coloured.
Ti⁺³ = [Ar]3d¹ one unpaired electron and hence coloured.