Question

Given below are two statements: Assertion (A): The bond angle in \(NH_3\) is smaller than the bond angle in \(CH_4\). Reason (R): \(NH_3\) contains one lone pair that repels bonding pairs more strongly than a bond pair.

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A)
• B. Both (A) and (R) are correct but (R) is not the correct explanation of (A)
• C. (A) is correct but (R) is not correct
• D. (A) is not correct but (R) is correct

Hint:

Lone pair-bond pair repulsion is stronger than bond pair-bond pair repulsion, so lone pairs reduce bond angles.

Answer 1

The Correct Option is A

Concept:
Bond angle is affected by electron pair repulsion. According to VSEPR theory, lone pair-bond pair repulsion is stronger than bond pair-bond pair repulsion.

Step 1: Bond angle in \(CH_4\).
Methane has tetrahedral geometry with bond angle: \[ 109.5^\circ \]

Step 2: Bond angle in \(NH_3\).
Ammonia has one lone pair on nitrogen. Due to this lone pair, the bond angle decreases to about: \[ 107^\circ \]

Step 3: Check Assertion.
Since \(107^\circ < 109.5^\circ\), the bond angle in \(NH_3\) is smaller than in \(CH_4\). \[ A \text{ is correct} \]

Step 4: Check Reason.
The lone pair in \(NH_3\) repels bonding pairs more strongly and compresses the bond angle. \[ R \text{ is correct} \]

Step 5: Check explanation.
The reason correctly explains why bond angle in \(NH_3\) is smaller than in \(CH_4\). \[ \therefore \text{Correct Answer is (A)} \]