Question

Electrolytic reduction of alumina to aluminium by Hall-Heroult process is carried out:

• A. in the presence of NaCl
• B. in the presence of fluorite
• C. in the presence of cryolite which forms a melt with a lower melting temperature
• D. in the presence of cryolite which forms a melt with a higher melting temperature

Answer 1

Answer: (B), (C)

The correct options are
B

in the presence of fluorite

C

in the presence of cryolite which forms a melt with a lower melting temperature

Cryolite is added to concentrated alumina so that the fusion temperature is lowered. Also, cryolite - $N{a}_{3}Al{F}_6$ - improves the conductivity of the melt.
Fluorspar - $Ca{F}_2$ (also called fluorite) is added to improve the conductivity.