AP Chemistrymediummcq1 pt
What is the oxidation number of phosphorus in K₃PO₄?
A.+5
B.+3
C.0
D.-3 (phosphide)
Explanation
Core Concept
Each potassium contributes +1 and each oxygen contributes -2. Setting the neutral formula unit's sum to zero gives 3(+1) + P + 4(-2) = 0, so phosphorus equals +5. Phosphate holds phosphorus at its highest common oxidation state. Solving for the unknown element after assigning the fixed ones works for any polyatomic-ion problem.
Correct Answer
A+5
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