Incorrect statement in electrolysis of Al2O3 by Hall-Heroult process is :
a. Cryolite Na3[AlF6] lowers the m.pt. of Al2O3 and increases its electrical conductivity
b. Al is obtained at cathode and CO2 at anode
c. Li2CO3 can be used in place of cryolite ( Na3AlF6 )
d. MgF2 can be used in place of flourspare ( CaF2 )