WAEC Chemistry 2015 Paper

Concept:Unpaired electrons are found by writing the electron configuration and applying Hund's rule.Explanation:The element $_{8}\mathrm{Q}$ has atomic number 8.Its electron configuration is $1s^{2}\,2s^{2}\,2p^{4}$.The $2p$ subshell contains three orbitals.According to Hund's rule, electrons occupy each orbital singly before pairing.So, the four electrons in the $2p$ subshell are arranged as one pair in one orbital and one unpaired electron in each of the other two orbitals.Therefore, the number of unpaired electrons is 2.Answer:A. 2