Explanation

(c)
In Down process, sodium is manufactured by the electrolysis of fused sodium chloride in the presence of $CaCl_{2}$ and KF using graphite anode and iron cathode.
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ NaCl\ \rightleftharpoons Na^{+} + Cl^{-}$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ Na^{+} + e^{-}\ \longrightarrow Na\ (at\ cathode)$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ 2Cl^{-}\ \rightarrow Cl_{2} + 2e^{-}(at\ anode)$
$CaCl_{2} + KF\$lower the melting point from the 1085 K to 850 K.