(i) Electrodes A and B are made of graphite (carbon).
(ii) Aluminium is formed at cathode (i.e., electrode A).
(iii) Fused alumina (Al2O3) and Cryolite (Na3AlF6) are the compounds in the electrolyte C.
(iv) The graphite [carbon] anodes (i.e electrode B) are continuously replaced during the electrolysis because :
- The oxygen evolved at the anode escapes as a gas or reacts with the carbon anode.
- The carbon anode is thus oxidized to carbon monoxide which either burns giving carbon dioxide or escapes out through an outlet. 2C + O2 ⟶ 2CO [2CO + O2 ⟶ 2CO2]
- The carbon anode is hence consumed and renewed periodically after a certain period of usage.