Why must the anodes be replaced from time to time during the electrolysis of fused alumina?

Ans.

1. During the electrolytic reduction of alumina, aluminium is produced at the cathode and oxygen gas is evolved at the anode.
2. This gas reacts with the graphite rods (anodes) and forms carbon dioxide.

Thus, the graphite rods are continuously eroded. Hence, the graphite rods i.e. anodes be replaced from time to time during the electrolysis of fused alumina.