Which of the following compound does not exist ?

Options

A. `NCl_(5)`
B. `AsF_(5)`
C. `SbCl_(5)`
D. `PF_(5)`

Explanation

To determine which of the given compounds does not exist, we need to analyze each option based on the chemistry of group 15 elements and their ability to form pentahalides.

### Step-by-Step Solution:

1. **Identify the Compounds**: The compounds given are NCl5, AsF5, SbCl5, and BF5. These are halides of group 15 elements.

2. **Understand Group 15 Elements**: Group 15 elements include nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), and bismuth (Bi). These elements can form various halides.

3. **Check for Pentahalides**: Most group 15 elements can form pentahalides (MX5), where M is the group 15 element and X is a halogen.

4. **Analyze Each Compound**:
- **NCl5 (Nitrogen Pentachloride)**: Nitrogen is in group 15 but it has no available d-orbitals to accommodate five chlorine atoms. Therefore, NCl5 cannot exist.
- **AsF5 (Arsenic Pentafluoride)**: Arsenic can form pentahalides because it has available d-orbitals. AsF5 exists.
- **SbCl5 (Antimony Pentachloride)**: Antimony also has d-orbitals and can form pentahalides. SbCl5 exists.
- **BF5 (Boron Pentafluoride)**: Although boron is not a group 15 element, it can form BF5. However, this compound is not relevant to the question since we are focusing on group 15 elements.

5. **Conclusion**: The only compound that does not exist among the options is NCl5.

### Final Answer:
The compound that does not exist is **NCl5**.