In following pairs, the one in which both transition metal ions are colourless is :
Solution
$\mathrm{Sc}^{+3}$ 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. <br/><br/>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.
About this question
Subject: Chemistry · Chapter: d and f Block Elements · Topic: Properties of Transition Metals
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