#### Answer

+4
+5
+5
+3

#### Work Step by Step

Recall that the oxidation number of O is usually 2-. Because the sum of the oxidation numbers in a compound must be 0, the oxidation number of P is +4.
Recall that the oxidation number of O is usually 2-. Because the sum of the oxidation numbers in this ion is 3- (given), the oxidation number of P is +5.
Recall that the oxidation number of O is usually 2-. Because the sum of the oxidation numbers in a compound must be 0, the oxidation number of P is +5.
Recall that the oxidation number of O is usually 2-. Because the sum of the oxidation numbers in a compound must be 0, the oxidation number of P is +3.