In the extraction of \(\mathrm{Ca}\) by electro reduction of molten \(\mathrm{CaCl}_{2}\) some \(\mathrm{CaF}_{2}\) is added to the electrolyte for the following reason:
(A) To keep the electrolyte in liquid state at temperature lower than the \(\mathrm{m}\). \(\mathrm{p} .\) of \(\mathrm{CaCl}_{2}\)
(B) To effect precipitation of \(\mathrm{Ca}\)
(C) To effect the electrolysis at lower voltage
(D) To increase the current efficiency
