The correct option is D 60 parts cryolite + 20 parts fluorspar + 20 parts pure Al2O3
Pure alumina melts at about 2000oC and is a bad conductor of electricity. If fused cryoliteand fluorspar is added, the mixture melts at 900oC and Al2O3 becomes a good conductorof electricity.
Electrolyte: 60 parts cryolite + 20 parts fluorspar + 20 parts pure Al2O3