In electrolysis of `A1_(2)O_(3)`by Hall-Heroult process:

Options

A. cryolite `Na_(3)[A1F_(6)]`lowers the melting point of `A1_(2)O_(3)`and increases its electrical conductivity.
B. `A1`is obtained at cathode and parobably `CO_(2)`at anode
C. both`(a)`and(b) are correct
D. none of the above is correct

Answer

C

Explanation

`Na_(3)[A1F_(6)] rarr 3NaF +A1F_(3)`
`NaF` and `A1F_(3)` both are ionic compounds and so ionise to give ions. The increases the electrical conductivity and lowers the melting point of `A1_(2)O_(3)`.
At cathode: `A1^(3+)("melt")+3e^(-) rarr A1.`
At anode: `C(s) +O^(2-) ("melt") rarr CO(g) +2e^(-)`,
`C(s) + 2O^(2-)("melt") rarr CO_(2)(g) +4e^(-1)`