Question

Assertion (A): ${\text{NH}}_3$ and ${\text{H}}_2\text{O}$ molecules are ${\text{sp}}^3$ hybridised, but the bond angle of ${\text{NH}}_3$ is more than that of ${\text{H}}_2\text{O}$.

Reason (R): Nitrogen atom has one lone pair whereas oxygen atom has two lone pairs of electrons.

• A. A and R both are correct and R is the correct explanation of A
• B. A and R both are correct and R is not the correct explanation of A
• C. A is correct and R is incorrect
• D. A is incorrect and R is correct

Answer 1

The correct option is A A and R both are correct and R is the correct explanation of A

Lone pair-lone pair repulsions > lone pair-bond pair repulsions > bond pair-bond pair repulsions.

$\bullet$ The presence of lone pair decreases the angle between the bonds.

$\bullet$ ${\text{NH}}_3$ has 3 bond pairs and one lone pair and the bond angle is ${\text{107.8}}^0$.

$\bullet$ In ${\text{H}}_2\text{O}$, there are 2 bond pairs and two lone pairs on the oxygen atom. Due to larger lone pair-lone pair repulsion the angle decreases more. Therefore, the bond angle of water molecule is 104.5 degrees.


Hence, both the assertion and reason are correct and reason is the correct explanation of assertion.