Here's why:

* Phosphorus (P) typically forms compounds with a +3 or +5 oxidation state.

* Chlorine (Cl) has a -1 oxidation state in most compounds.

To satisfy these oxidation states, the correct formula for a compound containing phosphorus and chlorine would be PCl5 (phosphorus pentachloride). In this compound, phosphorus has a +5 oxidation state and each chlorine atom has a -1 oxidation state.