Question

Let us consider a compound with molecular formula $M{X}_3$ having a lone pair in M. what will be the possible value of $\angle XMX$?

• A. Greater than ${120}^o$
• B. Greater than ${112}^o$
• C. Greater than ${109.5}^o$
• D. Less than ${109.5}^o$

Answer 1

The correct option is D Less than ${109.5}^o$

The given compound is $M{X}_3$ and it contains a lone pair in $M$.
Thus we have three $M-X$ bonds and a lone pair. Hence in $M{X}_3$, $M$ is $s{p}^3$ hybridized.
We know, the bond angle in $s{p}^3$ hybridised molecule should be ${109.5}^o$, but here since we have a lone pair on $M$ thus due to lone pair - bond pair repulsion the actual bond angle will be lower than ${109.5}^o$.
Thus the correct option for this question is (d).