In the extraction of aluminium by the Hall-Heroult process, purified Al2O3 is mixed with CaF2 to:

a. Lower the melting point of Al2O3
b. Increase the conductivity of the molten mixture.
c. Reduce Al3+into Als
d. Act as a catalyst

Choose the correct option:
1. a and b
2. b and c
3. c and d
4. a and d

HINT: CaF2 makes alumina a good conductor of electricity.
Explanation :
In the metallurgy of aluminium Al2O3 is mixed with Na3AlF6 and CaF2 which causes following affects.
(i) Lower the melting point of Al, O,   
(ii) Increase the conductivity of molten mixture