Electrolysis products in concentrated aqueous metal chloride Steps:

• The solution is concentrated XCl(aq), with X highly reactive (above Na in series), so cations X+ remain in solution.
• At the anode (oxidation), concentrated Cl⁻ ions are preferentially discharged over H₂O, producing Cl₂ gas.
• At the cathode (reduction), reactive X⁺ not discharged; instead, H₂O reduced to H₂ gas and OH⁻.
• Gases produced: Cl₂ at anode and H₂ at cathode; question asks for gas besides Cl₂.

Why D is correct:

• Hydrogen forms at cathode when metal ions are too reactive to be reduced, per electrochemical series rules.

Why the others are wrong:

• A: Anode involves oxidation (anions or water), not hydrogen production.
• B: Oxygen from water oxidation at anode only in dilute solutions or without halide ions.
• C: Cathode is reduction site; oxygen not produced there.

Final answer: D