Which of the following given molecules has all the bond angles equal to 120°?

Options

A. `CH_4`
B. `BF_3`
C. `BeCl_2`
D. `PCl_5`

Answer

To determine which of the given molecules has all bond angles equal to 120°, we will analyze each molecule one by one based on their hybridization and molecular geometry.

### Step-by-Step Solution:

1. **Identify the Molecules**: The molecules we need to analyze are Methane (CH₄), Boron Trifluoride (BF₃), Beryllium Chloride (BeCl₂), and Phosphorus Pentachloride (PCl₅).

2. **Analyze Methane (CH₄)**:
- **Valence Electrons**: Carbon has 4 valence electrons, and each hydrogen has 1 valence electron. Total = 4 + (4 × 1) = 8 valence electrons.
- **Bond Pairs and Lone Pairs**: There are 4 bond pairs and 0 lone pairs.
- **Steric Number**: Steric number = number of bond pairs + number of lone pairs = 4 + 0 = 4.
- **Hybridization**: The hybridization is sp³.
- **Molecular Geometry**: Tetrahedral with bond angles of approximately 109.5°.
- **Conclusion**: Not 120°.

3. **Analyze Boron Trifluoride (BF₃)**:
- **Valence Electrons**: Boron has 3 valence electrons, and each fluorine has 7 valence electrons. Total = 3 + (3 × 7) = 24 valence electrons.
- **Bond Pairs and Lone Pairs**: There are 3 bond pairs and 0 lone pairs.
- **Steric Number**: Steric number = 3 + 0 = 3.
- **Hybridization**: The hybridization is sp².
- **Molecular Geometry**: Trigonal planar with bond angles of 120°.
- **Conclusion**: All angles are 120°.

4. **Analyze Beryllium Chloride (BeCl₂)**:
- **Valence Electrons**: Beryllium has 2 valence electrons, and each chlorine has 7 valence electrons. Total = 2 + (2 × 7) = 16 valence electrons.
- **Bond Pairs and Lone Pairs**: There are 2 bond pairs and 0 lone pairs.
- **Steric Number**: Steric number = 2 + 0 = 2.
- **Hybridization**: The hybridization is sp.
- **Molecular Geometry**: Linear with bond angles of 180°.
- **Conclusion**: Not 120°.

5. **Analyze Phosphorus Pentachloride (PCl₅)**:
- **Valence Electrons**: Phosphorus has 5 valence electrons, and each chlorine has 7 valence electrons. Total = 5 + (5 × 7) = 40 valence electrons.
- **Bond Pairs and Lone Pairs**: There are 5 bond pairs and 0 lone pairs.
- **Steric Number**: Steric number = 5 + 0 = 5.
- **Hybridization**: The hybridization is sp³d.
- **Molecular Geometry**: Trigonal bipyramidal with bond angles of 90° and 120°.
- **Conclusion**: Not all angles are 120°.

### Final Conclusion:
The only molecule with all bond angles equal to 120° is **Boron Trifluoride (BF₃)**.