Although geometries of `NH_3` and `H_2O` molecules are distorted tetrahedral, bond angle in water is less than that of ammonia. This is due to

Options

A. lp-lp repulsion in `NH_3` and lp-bp repulsion in `H_2O`
B. lp-lp repulsion in `H_2O` and lp-bp repulsion in `NH_3`
C. bp-bp repulsion in `NH_3` and lp-bp repulsion in `H_2O`
D. None of the above

Answer

To solve the question regarding the bond angles in NH3 (ammonia) and H2O (water), we need to analyze the molecular geometry and the effects of lone pairs on bond angles.

### Step-by-Step Solution:

1. **Understanding Molecular Geometry**:
- Both NH3 and H2O have a distorted tetrahedral geometry due to the presence of lone pairs of electrons.
- NH3 has one lone pair and three bond pairs (N-H bonds).
- H2O has two lone pairs and two bond pairs (O-H bonds).

2. **Identifying Lone Pairs**:
- In NH3, the lone pair occupies one position in the tetrahedral arrangement, leading to a bond angle of approximately 107 degrees.
- In H2O, there are two lone pairs which occupy two positions, resulting in a smaller bond angle of approximately 104.5 degrees.

3. **Understanding Repulsion**:
- Lone pairs exert greater repulsive forces compared to bond pairs. This is because lone pairs are localized in space and occupy more volume than bonding pairs.
- The order of repulsion strength is: lone pair-lone pair > lone pair-bond pair > bond pair-bond pair.

4. **Comparing Bond Angles**:
- The presence of two lone pairs in H2O leads to increased lone pair-lone pair repulsion, which pushes the O-H bonds closer together, thereby reducing the bond angle.
- In contrast, NH3 has only one lone pair, which results in less repulsion and a larger bond angle compared to H2O.

5. **Conclusion**:
- The bond angle in water is less than that in ammonia due to the increased lone pair-lone pair repulsion in H2O compared to the lone pair-bond pair repulsion in NH3.

### Final Answer:
The bond angle in water is less than that in ammonia due to the lone pair-lone pair repulsion in water and lone pair-bond pair repulsion in ammonia.