During the electrolysis of fused carnalite, ${\mathrm{MgCI}}_2$ is decomposed to liberate Mg at cathode and not KCI to liberate the Kat cathode. This is because of:

In contrast to KCI, magnesium chloride would have released cathode during the electrolysis of fused carnalite, ${\mathrm{MgCI}}_2$ is broken down to release Mg at the cathode. This is due to ${\mathrm{MgCI}}_2$’s lower decomposition voltage when compared to KCl.

Hence the correct option is A.