`PCl_(5)` is known but `NCl_(5)` is not known.
Or Nitrogen does not form pentahalide.

Explanation

To understand why phosphorus forms pentachloride (PCl₅) while nitrogen does not form pentachloride (NCl₅), we can analyze the electronic configurations and the availability of orbitals for bonding.

### Step-by-Step Solution:

1. **Electronic Configuration of Phosphorus (P)**:
- Phosphorus has an atomic number of 15. Its electronic configuration is:
\[
1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^3
...