Which of the following statements is incorrect regarding the electrolysis of $Al_2O_3$ by the Hall-Heroult process?

• A
  Cryolite $(Na_3AlF_6)$ lowers the melting point of $Al_2O_3$ and increases its electrical conductivity.
• B
  $Al$ is obtained at the cathode and $CO_2$ is obtained at the anode.
• C
  $Li_2CO_3$ can be used in place of cryolite $(Na_3AlF_6)$.
• D
  $MgF_2$ can be used in place of fluorspar $(CaF_2)$.