Q.Electrochemical process is used in the extraction of which of the following element ?

Highly electropositive metals like sodium cannot be won from their ores by chemical reduction (with carbon or another metal), because no ordinary reducing agent is powerful enough; they are instead extracted electrochemically, by electrolysing their molten (fused) salt.

The method used to extract a metal from its ore depends on the metal's reactivity/position in the electrochemical series. Highly reactive metals (Na, K, Ca, Mg, Al) form very stable compounds that are extremely difficult to reduce chemically, so they are extracted by the electrochemical (electrolytic) process — electrolysis of their molten salts or oxides. Sodium is specifically extracted by the electrolysis of fused (molten) sodium chloride, mixed with a little $CaCl_2$ to lower its melting point, in a Down's cell: $NaCl \xrightarrow{\text{electrolysis (fused)}} Na\ (\text{at cathode}) + \dfrac{1}{2}Cl_2\ (\text{at anode})$ Iron and lead, being moderately reactive, are extracted by thermal/chemical re …