When electricity is passed through an aqueous solution of sodium chloride, it decomposes to form

The correct answer is B, NaOH. When an electric current is passed through brine, a concentrated aqueous solution of sodium chloride, the salt decomposes. Chlorine gas is given off at the anode and hydrogen gas at the cathode, while sodium hydroxide is left in the solution near the cathode. The overall reaction is 2NaCl + 2H2O gives 2NaOH + Cl2 + H2. This is the chlor-alkali process, named after its two main products, chlorine and alkali (caustic soda). All three products are useful: sodium hydroxide for soaps, paper and textiles; chlorine for PVC, disinfecting water and making bleaching powder; and hydrogen as a fuel and for making ammonia. Option A is wrong because NaHCO3, baking soda, is made by the Solvay process using carbon dioxide and ammonia. Option C is wrong because hydrochloric acid is made by combining hydrogen and chlorine later, not formed directly in the cell. Option D is wrong because hypochlorous acid forms when chlorine dissolves in water, not as the electrolysis product. Exam tip: chlor-alkali process: brine gives NaOH, Cl2 at the anode, H2 at the cathode.