Electrolysis Gas Production in NaCl Solutions

Steps:

• Concentrated NaCl electrolysis: Cathode produces H₂ (2H₂O + 2e⁻ → H₂ + 2OH⁻), anode produces Cl₂ (2Cl⁻ → Cl₂ + 2e⁻); equal moles of gas per electrons passed, so equal volumes in W and X.
• Dilute NaCl electrolysis: Cathode produces H₂ (same reaction), anode produces O₂ (4OH⁻ → O₂ + 2H₂O + 4e⁻); H₂:O₂ volume ratio 2:1, but approximately equal volumes collected in Y and Z per diagram conditions.
• Both experiments produce H₂; concentrated also yields Cl₂, confirming statement 3 on gases including those in Z.

Why D is correct:

• Faraday's first law states gas volume proportional to charge passed; equal electron requirement (2e⁻ per mol gas) for H₂ and Cl₂ ensures equal volumes, while dilute approximation and gas production validate all statements.

Why the others are wrong:

• A omits statement 3 on gas production.
• B omits statement 1 on equal volumes in W and X.
• C omits statement 2 on approximate equality in Y and Z.

Final answer: D