Question

Which among of the following pairs has the bond angle ${109}^{\circ }{28}^{\prime }$?

• A. $\left[N{H}_4^{+}\right],\left[{BF}_4^{-}\right]$
• B. $\left[N{H}_4^{+}\right],\left[B{F}_3\right]$
• C. $N{H}_3,\left[{BF}_4^{-}\right]$
• D. $\left[N{H}_3\right],\left[B{F}_3\right]$

Answer 1

The correct option is A $\left[N{H}_4^{+}\right],\left[{BF}_4^{-}\right]$

Each bond angle in a perfect tetrahedral structure is $109°{28}^{\prime }$.

Any species which forms a perfect tetrahedral structure will have $s{p}^3$ hybridized central atom with $4$ bp.

$4$ bps are necessary as presence of lone pair will slightly reduce the bond angle.

For possibility of $4$ bp, there must be $4$ monovalent side atoms in each molecule

Hence, only possible pair is $\left[N{H}_4^{+}\right]$, $\left[B{F}_4^{-}\right]$