Which of the following the molecule (s) has/have back bonding ?

Options

A. `N(SiH_(3))_(3)`
B. `BF_(3)`
C. `O Cl_(2)`
D. `BF_(4)^(-)`

Answer

To determine which of the given molecules has back bonding, we need to analyze each molecule based on the presence of lone pairs and vacant orbitals. Back bonding occurs when a lone pair from one atom can be donated to an empty orbital of another atom, forming a π bond. Let's go through the analysis step by step.

### Step-by-Step Solution:

1. **Identify the Molecules**:
- We need to analyze the given molecules one by one to check for back bonding.

2. **First Molecule**:
- The first molecule has a pyramidal shape initially.
- Upon considering back bonding, the shape changes to a trigonal planar configuration.
- There is a lone pair on the atom and a vacant orbital that can align parallel to the lone pair.
- **Conclusion**: This molecule exhibits back bonding.

3. **Second Molecule**:
- The second molecule is linear in structure.
- Boron has a vacant orbital, and chlorine has a lone pair.
- The lone pair from chlorine can be donated to the vacant orbital of boron.
- **Conclusion**: This molecule also exhibits back bonding.

4. **Third Molecule**:
- The third molecule initially has a bent shape.
- For back bonding to occur, the structure must be linear.
- Chlorine has a vacant 3d orbital and a lone pair that can participate in back bonding.
- **Conclusion**: This molecule exhibits back bonding as well.

5. **Fourth Molecule**:
- In the fourth molecule, boron is already making four bonds.
- Since boron has no vacant orbitals available, back bonding cannot occur.
- **Conclusion**: This molecule does not exhibit back bonding.

### Final Answer:
- The first, second, and third molecules exhibit back bonding, while the fourth molecule does not.