The oxidation state of phosphorus (P) in PCl5 is +5. Here's how to determine that:

* Chlorine (Cl) is a halogen and typically has an oxidation state of -1.

* In PCl5, there are five chlorine atoms, giving a total oxidation state of -5 for chlorine.

* The overall charge of the molecule is neutral (zero).

* To balance the -5 charge from chlorine, the phosphorus atom must have an oxidation state of +5.

Therefore, the oxidation state of phosphorus in PCl5 is +5.