Anode reaction in concentrated NaCl electrolysis

Steps:

• Anode is site of oxidation, releasing electrons.
• In concentrated aqueous NaCl, anions present are Cl⁻ (from NaCl) and OH⁻ (from water).
• Concentrated Cl⁻ makes its oxidation (lower potential, 1.36 V) more likely than water's (1.23 V but overpotential favors Cl⁻).
• Thus, 2Cl⁻ discharge to Cl₂ occurs.

Why A is correct:

• Matches oxidation half-reaction for Cl⁻ ions, as per standard electrode potentials where Cl₂/Cl⁻ (1.36 V) is discharged preferentially in high [Cl⁻].

Why the others are wrong:

• B: Water oxidation to O₂ occurs in dilute NaCl, not concentrated.
• C: Cathode reduction of H⁺ to H₂, not anode oxidation.
• D: OH⁻ oxidation to O₂ in basic conditions or dilute solutions, not concentrated Cl⁻.

Final answer: A