Question

`Sc^(3+)` is colourless is aqueous solution whereas `Ti^(3+)` is coloured.

Answer 1

Electronic configuration of `._(21)Sc^(3+)` is [Ar `3d^(0)` and `._(22)Ti^(3+)` is [Ar] `3d^(1)`.
Therefore due to absence of unpaired electron `Sc^(3+)` is colourless and due to presence of one unpaired electron d-d transtion takes place hence `Ti^(3+)` is coloured.