Explain the electrolytic reduction of alumina.

(N/A) In the electrolytic reduction of aluminium,purified $Al_{2}O_{3}$ is mixed with $Na_{3}AlF_{6}$ (cryolite) or $CaF_{2}$ (fluorspar),which lowers the melting point of the mixture and increases its electrical conductivity.
This mixture is electrolysed in a steel vessel with a carbon lining that acts as the cathode,while graphite rods act as the anode.
The overall process is represented by the equation:
$2Al_{2}O_{3} + 3C \rightarrow 4Al + 3CO_{2}$
During electrolysis,oxygen gas is liberated at the anode,which reacts with the carbon of the anode to form $CO$ and $CO_{2}$.
For every $1 \ kg$ of aluminium produced,approximately $0.5 \ kg$ of the carbon anode is consumed. Therefore,the graphite anodes need to be replaced periodically.
Cathode reaction: $Al^{3+} + 3e^{-} \rightarrow Al_{(l)}$
Anode reactions:
$C_{(s)} + O^{2-} \rightarrow CO_{(g)} + 2e^{-}$
$C_{(s)} + 2O^{2-} \rightarrow CO_{2(g)} + 4e^{-}$