In which of the following molecules, central atom is not `sp^2` hybridize

Options

A. `BeCl_2`
B. `BCl_3`
C. NH_3
D. `ClF_3`

Answer

To determine which of the following molecules has a central atom that is not sp² hybridized, we will analyze the hybridization of each molecule based on the steric number. The steric number is calculated as the sum of the number of sigma bonds and the number of lone pairs on the central atom.

### Step-by-Step Solution:

1. **Identify the Molecules**: We need to check the hybridization of the central atom in the following molecules: BeCl₂, BCl₃, NH₃, and ClF₃.

2. **Calculate Hybridization for BeCl₂**:
- **Valence Electrons**: Beryllium (Be) has 2 valence electrons.
- **Bonds**: It forms 2 sigma bonds with 2 chlorine atoms (Cl).
- **Lone Pairs**: There are no lone pairs on Be.
- **Steric Number**: 2 (2 sigma bonds + 0 lone pairs).
- **Hybridization**: The steric number of 2 corresponds to sp hybridization.

3. **Calculate Hybridization for BCl₃**:
- **Valence Electrons**: Boron (B) has 3 valence electrons.
- **Bonds**: It forms 3 sigma bonds with 3 chlorine atoms.
- **Lone Pairs**: There are no lone pairs on B.
- **Steric Number**: 3 (3 sigma bonds + 0 lone pairs).
- **Hybridization**: The steric number of 3 corresponds to sp² hybridization.

4. **Calculate Hybridization for NH₃**:
- **Valence Electrons**: Nitrogen (N) has 5 valence electrons.
- **Bonds**: It forms 3 sigma bonds with 3 hydrogen atoms.
- **Lone Pairs**: There is 1 lone pair on N.
- **Steric Number**: 4 (3 sigma bonds + 1 lone pair).
- **Hybridization**: The steric number of 4 corresponds to sp³ hybridization.

5. **Calculate Hybridization for ClF₃**:
- **Valence Electrons**: Chlorine (Cl) has 7 valence electrons.
- **Bonds**: It forms 3 sigma bonds with 3 fluorine atoms.
- **Lone Pairs**: There are 2 lone pairs on Cl.
- **Steric Number**: 5 (3 sigma bonds + 2 lone pairs).
- **Hybridization**: The steric number of 5 corresponds to sp³d hybridization.

### Conclusion:
From the calculations:
- BeCl₂: sp hybridized
- BCl₃: sp² hybridized
- NH₃: sp³ hybridized
- ClF₃: sp³d hybridized

The central atom that is **not sp² hybridized** is found in BeCl₂, NH₃, and ClF₃. Therefore, the answer is that the central atom in BeCl₂, NH₃, and ClF₃ is not sp² hybridized.