JAMB Chemistry 2024 Paper

Concept:A transition metal must form an ion with a partially filled $d$-orbital. Scandium does not meet this condition because its common ion has an empty $d$-subshell.Explanation:Scandium has the electronic configuration $\mathrm{[Ar]}\,3d^1\,4s^2$.When it forms its most stable ion, $\mathrm{Sc}^{3+}$, it loses the two $4s$ electrons and the single $3d$ electron.The resulting $\mathrm{Sc}^{3+}$ ion has the configuration $\mathrm{[Ar]}$, meaning there are no electrons in the $d$-orbital.Since the $d$-orbital is completely empty, $\mathrm{Sc}^{3+}$ cannot exhibit the characteristic properties of transition metals, such as coloured ions and variable oxidation states.Therefore, scandium is excluded from the transition metals because its ion has no electron in the $d$-orbital.Answer:A. no electron in the $d$-orbital