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, AsF5, and SbF5, we can analyze the electronic configurations and the ability of these elements to form stable compounds.

### Step-by-Step Solution:

1. **Identify the Elements and Their Electronic Configurations**:
- **Nitrogen (N)**: Electronic configuration is 1s² 2s² 2p³.
- **Phosphorus (P)**: Electronic configuration is [Ne] 3s² 3p³.
- **Arsenic (As)**: Electronic configuration is [Ar] 3d¹⁰ 4s² 4p³.
- **Antimony (Sb)**: Electronic configuration is [Kr] 4d¹⁰ 5s² 5p³.

2. **Analyze the Ability to Form Compounds**:
- **NF5**: Nitrogen has no d-orbitals available (it is in the second period), which limits its ability to expand its coordination number beyond four. Therefore, NF5 cannot exist.
- **PF5**: Phosphorus can utilize its 3d orbitals to accommodate five fluorine atoms, allowing it to form PF5.
- **AsF5**: Arsenic can also use its 4d orbitals to form AsF5.
- **SbF5**: Antimony can use its 5d orbitals to form SbF5.

3. **Conclusion**:
- Among the compounds listed, NF5 is the only one that cannot exist in nature due to the absence of d-orbitals in nitrogen, which prevents it from accommodating five fluorine atoms.

### Final Answer:
**NF5 does not exist in nature.**