Which one of the following fluorides does not exist in nature ?

Options

A. `NF_5`
B. `PF_5`
C. `AsF_5`
D. `SbF_5`

Answer

To determine which fluoride does not exist in nature among NF5, PF5, SF5, and SbF5, we can analyze the bonding capabilities of the respective central atoms based on their electronic configurations.

### Step-by-Step Solution:

1. **Identify the Elements and Their Groups**:
- NF5 (Nitrogen fluoride) - Nitrogen (N) belongs to Group 15.
- PF5 (Phosphorus fluoride) - Phosphorus (P) also belongs to Group 15.
- SF5 (Sulfur fluoride) - Sulfur (S) belongs to Group 16.
- SbF5 (Antimony fluoride) - Antimony (Sb) belongs to Group 15.

2. **Determine the Valence Electrons**:
- Nitrogen (N): 2s² 2p³ (5 valence electrons)
- Phosphorus (P): 3s² 3p³ (5 valence electrons)
- Sulfur (S): 3s² 3p⁴ (6 valence electrons)
- Antimony (Sb): 5s² 5p³ (5 valence electrons)

3. **Consider the Maximum Covalency**:
- Nitrogen has no d-orbitals available for bonding, thus it can only form a maximum of 3 bonds (covalency of 3).
- Phosphorus can utilize its d-orbitals to form up to 5 bonds (covalency of 5).
- Sulfur can also utilize its d-orbitals to form multiple bonds.
- Antimony, like phosphorus, can utilize its d-orbitals to form up to 5 bonds.

4. **Evaluate Each Compound**:
- **NF5**: Nitrogen cannot form 5 bonds due to the lack of d-orbitals; hence, NF5 does not exist.
- **PF5**: Phosphorus can form 5 bonds; PF5 exists.
- **SF5**: Sulfur can also form 5 bonds; SF5 exists.
- **SbF5**: Antimony can form 5 bonds; SbF5 exists.

5. **Conclusion**:
- The fluoride that does not exist in nature is **NF5**.