Give the electrolytic reaction of $CuSO_4$ solution using $Cu$ electrodes.

• A
  At anode: $Cu(s) \rightarrow Cu^{2+}(aq) + 2e^-$; At cathode: $Cu^{2+}(aq) + 2e^- \rightarrow Cu(s)$
• B
  At anode: $2H_2O(l) \rightarrow O_2(g) + 4H^+(aq) + 4e^-$; At cathode: $Cu^{2+}(aq) + 2e^- \rightarrow Cu(s)$
• C
  At anode: $Cu(s) \rightarrow Cu^{2+}(aq) + 2e^-$; At cathode: $2H_2O(l) + 2e^- \rightarrow H_2(g) + 2OH^-(aq)$
• D
  At anode: $2SO_4^{2-}(aq) \rightarrow S_2O_8^{2-}(aq) + 2e^-$; At cathode: $Cu^{2+}(aq) + 2e^- \rightarrow Cu(s)$