In the preparation of chlorine by the electrolysis of brine, the reaction taking place at the anode is

• A
  $Cl^{-}_{(aq)} \rightarrow \frac{1}{2} Cl_{2(g)} + e^{-}$
• B
  $Na^{+}_{(aq)} + e^{-} \rightarrow Na_{(s)}$
• C
  $O_{2(g)} + 4H^{+} + 4e^{-} \rightarrow 2H_{2}O_{(l)}$
• D
  $H^{+}_{(aq)} + e^{-} \rightarrow \frac{1}{2} H_{2(g)}$