In the electrolysis of aqueous sodium chloride solution, which of the half-cell reactions will occur at the anode?
a) Cl⁻ → Cl₂ + 2e⁻
b) Na⁺ + e⁻ → Na
c) 2H₂O → O₂ + 4H⁺ + 4e⁻
d) 2Cl⁻ → 2e⁻ + Cl₂