Which of the following has the least bond angle ?

Options

A. `NH_(3)`
B. `BeF_(2)`
C. `H_(2)O`
D. `CH_(4)`

Answer

To determine which of the given molecules has the least bond angle, we will analyze each option based on their molecular geometry and the presence of lone pairs of electrons.

### Step-by-Step Solution:

1. **Identify the Molecules and Their Structures**:
- **Ammonia (NH₃)**: Nitrogen has 5 valence electrons, forming 3 bonds with hydrogen and having 1 lone pair.
- **Beryllium Fluoride (BeF₂)**: Beryllium has 2 valence electrons and forms 2 bonds with fluorine. The structure is linear.
- **Water (H₂O)**: Oxygen has 6 valence electrons, forming 2 bonds with hydrogen and having 2 lone pairs.
- **Methane (CH₄)**: Carbon has 4 valence electrons and forms 4 bonds with hydrogen, having no lone pairs.

2. **Determine the Bond Angles**:
- **Ammonia (NH₃)**: The bond angle is approximately 107° due to the presence of 1 lone pair which repels the bond pairs.
- **Beryllium Fluoride (BeF₂)**: The bond angle is 180° as it is a linear molecule with no lone pairs.
- **Water (H₂O)**: The bond angle is approximately 104.5° due to the presence of 2 lone pairs which exert greater repulsion on the bond pairs.
- **Methane (CH₄)**: The bond angle is 109.5° as it has a perfect tetrahedral geometry with no lone pairs.

3. **Compare the Bond Angles**:
- Ammonia: 107°
- Beryllium Fluoride: 180°
- Water: 104.5°
- Methane: 109.5°

4. **Identify the Least Bond Angle**:
- Among the calculated bond angles, water (H₂O) has the least bond angle of 104.5°.

### Conclusion:
The molecule with the least bond angle among the given options is **Water (H₂O)**.