In the electrolysis of alumina to obtain aluminium metal, cryolite is added mainly to

During the Hall-Héroult electrolytic extraction of aluminium, pure $$Al_2O_3$$ (melting point $$\approx 2050^{\circ}\text{C}$$) cannot be fused economically on its own.

Molten cryolite, $$Na_3AlF_6$$, is therefore added. Its principal effect is to form a solution with alumina whose melting point is far lower (around $$950^{\circ}\text{C}$$). This reduction in operating temperature slashes fuel costs and prevents rapid corrosion of the carbon electrodes.

Cryolite does incidentally increase the melt’s electrical conductivity, yet that is a secondary benefit; the industrial process would be impossible without first lowering the fusion temperature of alumina.

Hence the main purpose of adding cryolite is to lower the melting point of alumina.

Option A which is: lower the melting point of alumina