JAMB Chemistry 2020 Paper

Concept:Unpaired electrons are found when an orbital is not completely filled, especially in partially filled subshells.Explanation:The configuration is $\mathrm{1s^2\,2s^2\,2p^6\,3s^2\,3p^3}$.The subshells $1s$, $2s$, $2p$, and $3s$ are completely filled, so they contain no unpaired electrons.The $3p$ subshell has three orbitals and can hold up to six electrons.Only three electrons occupy the $3p$ subshell in this element.By Hund's rule, electrons fill each $3p$ orbital singly before pairing begins.Therefore, each of the three $3p$ electrons occupies a different orbital, giving three unpaired electrons.Answer:C. 3