QJEEM22Ch5067: JEE Main 2022 Chemistry - Class 12 JEEM22Ch5067 Solution: In following pairs, the one in which both transition metal ions …

$\mathrm{Sc}^{+3}$ and $\mathrm{Zn}^{+2}$ are colourless as they contain no unpaired electron. Whereas the transition metal ions $\mathrm{Cu}^{+2}, \mathrm{Ti}^{+3}, \mathrm{~V}^{+2}$ and $\mathrm{Mn}^{+2}$ are coloured as they contain unpaired electrons.

The unpaired electron from lower energy $d$ orbital gets excited to a higher energy $d$ orbital on absorbing light of frequency which lies in visible region. The colour complementary to light absorbed is observed.