In the metallurgy of aluminium:

 1 Al3+ is oxidised to Al(s). 2 The graphite anode is oxidised to carbon monoxide and carbon dioxide. 3 Oxidation state of oxygen change in the reaction at the anode. 4 The oxidation state of oxygen changes in the overall reaction involved in the process.

HINT: Graphite anode is oxidised to carbon monoxide and carbon dioxide.

Explanation:

STEP 1:
In the metallurgy of aluminium, electrolysis is performed in a steel vessel with the lining of carbon acting as cathode and graphite act as an anode.
During this process, graphite anode is oxidised to $\mathrm{CO}$ and ${\mathrm{CO}}_{2}$.
The chemical reaction occurring in this process is as follows:
STEP 2:
This process is known as the Hall-Heroult process.
The electrolytic reactions are:
At cathode;
At anode;