Question

why concentrated sodium chloride is used in the manufacture of chlorine by electrolysis method ?

Answer 1

In electrolysis of conc. NaCl, the ions ppresent are Na⁺, H⁺, OH^- and Cl^-

Although OH is easier to discharge at anode, but due to high concentration of Cl^- loses electrons at anode to become Cl atom. These Cl atoms form covalent bond together to make Cl₂ gas.