* Phosphorus (P) typically has an oxidation number of +3 or +5.

* Chlorine (Cl) typically has an oxidation number of -1.

Let's use the rules of oxidation numbers:

1. The sum of the oxidation numbers in a neutral molecule must equal zero.

2. The oxidation number of a monatomic ion is equal to its charge.

Setting up the equation:

Let x represent the oxidation number of Cl.

P + 4x = 0

Solving for x:

* Since P has an oxidation number of +5 in this compound:

+5 + 4x = 0

* 4x = -5

* x = -5/4

Therefore, the oxidation number of Cl in PCl₄ is -5/4.

Important Note: While this calculation is technically correct, it's unusual for chlorine to have a fractional oxidation number. This suggests that PCl₄ may not exist as a stable compound with all Cl atoms having the same oxidation state.