When electricity is passed through an aqueous solution of sodium chloride it decomposes to form sodium hydroxide. The process is called the chlor-alkali alkali process.
An aqueous solution of sodium chloride is called brine.
2NaCl (aq) + 2H2O(l) (electrolysis) → 2NaOH(aq) + Cl2(g) + H2(g).
Chlorine gas is given off at anode and hydrogen gas at cathode.