C-10-Q094mediumsingle_mcqAt the anode of copper refining, the reaction is—aCu→Cu2++2e−\mathrm{Cu \to Cu^{2+} + 2e^-}Cu→Cu2++2e− (oxidation)bCu2++2e−→Cu\mathrm{Cu^{2+} + 2e^- \to Cu}Cu2++2e−→Cuc2H++2e−→H2\mathrm{2H^+ + 2e^- \to H_2}2H++2e−→H2dO2+4e−→2O2−\mathrm{O_2 + 4e^- \to 2O^{2-}}O2+4e−→2O2−