In the electrolysis of molten alumina during the manufacture of aluminium:

Cryolite undergoes dissociation during electrolysis of molten alumina during the manufacture of aluminum as,

${\mathrm{Na}}^{+}$and ${\mathrm{AIF}}_{6}3-$ ions are entirely separated from cryolite. At 1000 °C, the latter further partially dissociates into ${\mathrm{AlF}}_4^{-}$ and F ions to a degree of around 25%. The addition of aluminum fluoride will cause the melted Fluorine ions to react with one another to create ${\mathrm{AlF}}_4^{-}$ions.

Hence Correct option is B.