Which of the following chemical reactions occurs at the anode during the electrolysis of a highly concentrated $H_2SO_4$ solution?

• A
  $2SO_4^{2-}{_{\text{(aq)}}} \rightarrow S_2O_8^{2-}{_{\text{(aq)}}} + 2e^{-}$
• B
  $2H_2O_{(l)} \longrightarrow O_{2(g)} + 4H^{+}_{(aq)} + 4e^-$
• C
  $H_2O_{(l)} + e^- \longrightarrow \frac{1}{2}H_{2(g)} + OH^{-}_{(aq)}$
• D
  $S_2O_8^{2-}{_{\text{(aq)}}} + 2e^{-} \rightarrow 2SO_4^{2-}{_{\text{(aq)}}}$