In which of the following molecules, central atom is `sp^2` hybridized

Options

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

Answer

To determine which of the given molecules has a central atom that is sp² hybridized, we will analyze each option step by step.

### Step 1: Identify the molecules
The given options are:
1. Barium dichloride (BaCl₂)
2. Boron trichloride (BCl₃)
3. Ammonia (NH₃)
4. Chlorine trifluoride (ClF₃)

### Step 2: Analyze each molecule for hybridization

#### Option 1: Barium dichloride (BaCl₂)
- **Valence Electrons**: Barium has 2 valence electrons and each chlorine has 7, giving a total of 2 + 2(7) = 16 valence electrons.
- **Structure**: Barium is a metal and forms ionic bonds with chlorine. The structure is linear.
- **Hybridization**: The central atom (Ba) does not undergo hybridization in ionic compounds. Thus, BaCl₂ is not sp² hybridized.

**Hint**: Look for the type of bonding (ionic vs covalent) to determine hybridization.

#### Option 2: Boron trichloride (BCl₃)
- **Valence Electrons**: Boron has 3 valence electrons and each chlorine has 7, giving a total of 3 + 3(7) = 24 valence electrons.
- **Structure**: Boron forms three covalent bonds with chlorine atoms.
- **Hybridization**: The steric number is 3 (3 sigma bonds, no lone pairs), which corresponds to sp² hybridization. Thus, BCl₃ is sp² hybridized.

**Hint**: Count the number of sigma bonds and lone pairs to determine the steric number.

#### Option 3: Ammonia (NH₃)
- **Valence Electrons**: Nitrogen has 5 valence electrons and each hydrogen has 1, giving a total of 5 + 3(1) = 8 valence electrons.
- **Structure**: Nitrogen forms three covalent bonds with hydrogen and has one lone pair.
- **Hybridization**: The steric number is 4 (3 sigma bonds and 1 lone pair), which corresponds to sp³ hybridization. Thus, NH₃ is not sp² hybridized.

**Hint**: Remember that lone pairs also contribute to the steric number.

#### Option 4: Chlorine trifluoride (ClF₃)
- **Valence Electrons**: Chlorine has 7 valence electrons and each fluorine has 7, giving a total of 7 + 3(7) = 28 valence electrons.
- **Structure**: Chlorine forms three bonds with fluorine and has two lone pairs.
- **Hybridization**: The steric number is 5 (3 sigma bonds and 2 lone pairs), which corresponds to sp³d hybridization. Thus, ClF₃ is not sp² hybridized.

**Hint**: Check the number of lone pairs and bonds to find the hybridization.

### Conclusion
The only molecule among the options that has a central atom that is sp² hybridized is **Boron trichloride (BCl₃)**.

### Final Answer
**Boron trichloride (BCl₃)** is the molecule in which the central atom is sp² hybridized.

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