In this reaction:Cu s + 4HNO3 aq Cu NO3 2 aq + 2NO2 g + 2H2O l To identify the oxidizing and reducing agents, we need to determine the changes in oxidation states of the elements involved in the reaction.1. Copper Cu changes from an oxidation state of 0 in Cu s to +2 in Cu NO3 2 aq . This is an increase in oxidation state, which means Cu is being oxidized. Therefore, Cu s is the reducing agent.2. Nitrogen N changes from an oxidation state of +5 in HNO3 aq to +4 in NO2 g . This is a decrease in oxidation state, which means N is being reduced. Therefore, HNO3 aq is the oxidizing agent.