Give reasons. Sc3+ is colourless in aqueous solution whereas Ti3+ is coloured.

Transition metal ions are colored due to d-d transition. Unpaired electrons in d orbitals are excited from lower energy level to higher energy level. For this, energy from the visible region is absorbed. Sc3+ has an outer electronic configuration of 3d04s0 with zero unpaired electrons. Hence, it is colorless. Ti3+ has an outer electronic configuration of 3d14s0 with one unpaired electron. Hence, it is purple colored.