
In this reaction, Cu is reduced from +1 state to zero. oxidation state and S is oxidised from -2 state to +4 state. Cu2O helps S in Cu2S to increase its oxidation number. Therefore, Cu(l) is the oxidising agent. S of Cu2S helps Cu both in Cu2S itself and Cu2O to decrease its oxidation number. Therefore, S of Cu2S is the reducing agent.