WAEC Chemistry 2014 Paper

Concept:A lone pair of electrons is a pair of valence electrons not shared with another atom in a covalent bond.Explanation:In the hydrogen fluoride ($\mathrm{HF}$) molecule, fluorine contributes the valence electrons available for bonding.Fluorine has $7$ valence electrons in total.Hydrogen has $1$ valence electron and shares it with fluorine to form a single covalent bond.During bond formation, fluorine uses only $1$ of its valence electrons to share with hydrogen.Therefore, the remaining $6$ valence electrons on fluorine stay as three non-bonding pairs.Hydrogen does not have any lone pair because it shares its only electron.Hence, $\mathrm{HF}$ contains exactly $3$ lone pairs of electrons on fluorine.Answer:$3$ lone pairs of electrons are present in $\mathrm{HF}$.Correct option: D.