Answer:+5
Step-by-step explanation:
The oxidation number of the phosphorus (P) in phosphate (PO₄³⁻) is +5.
This is because oxygen (O) has an oxidation number of -2 and there are four oxygen atoms in the phosphate ion, giving a total charge of -8. Since the overall charge of the ion is -3, this means that the oxidation state of phosphorus must be +5 to account for the total charge of the ion.