Which of the following isolated, completely gaseous transition metal complex cations is mathematical — d and f Block Elements Chemistry Question

💡 Solution & Explanation

The generation of typical transition metal colors requires the presence of at least one unpaired $d$ -electron to undergo excitation ($d-d$ transition) upon absorbing visible light. Scandium ($Sc$, $Z=21$) has a ground state configuration of $[Ar] 3d^1 4s^2$. When it forms a $Sc^{3+}$ ion, it loses all three valence electrons, resulting in an empty $3d^0$ subshell (a complete $[Ar]$ noble gas core). Without any $d$ -electrons, no $d-d$ transitions can occur, rendering the ion colourless.