Final answer:
In the given reaction, HNO₃ is oxidized and serves as the oxidizing agent, while P₄ is not reduced and is not an oxidizing or reducing agent.
Step-by-step explanation:
In the reaction: PA + HNO₃ → H₃PO₄ + NO₂ + H₂O, the HNO₃ is oxidized. This is because the oxidation state of nitrogen increases from +5 in HNO₃ to +4 in NO₂.
The oxidizing agent is the species that causes oxidation, and in this case, HNO₃ is the oxidizing agent.
On the other hand, P₄ is not involved in any oxidation or reduction process in this reaction, so it is not reduced and is not an oxidizing or reducing agent.