The correct option is C in the presence of cryolite which forms a melt with lower melting temperature
The electrolysis of pure alumina faces some difficulties. Pure alumina is a bad conductor of electricity. The fusion temperature of pure alumina is about 2000∘C and at this temperature when electrolysis is carried out on the fused mass, the metal formed vaporizes, as the boiling point of aluminium is 1800∘C. These difficulties are overcome by using a mixture containing alumina, cryolite (Na3.AlF6), and fluorspar (CaF2) which forms a melt with lower melting temperature.