Sodium chloride solution is electrolysed using inert electrodes. Explain why chlorine gas is produced at the anode rather than oxygen, and identify the product formed at the cathode, explaining why that product forms instead of sodium metal.

At the anode the oxidation reaction occurs. The solution contains chloride ions, which are negatively charged. The anode is the positive electrode, so chloride ions are attracted to it and lose electrons:
Cl⁻ → ½Cl₂ + e⁻
Thus chlorine gas is produced.
At the cathode reduction takes place. The solution also contains hydrogen ions (from water). Electrons are supplied to the hydrogen ions, giving hydrogen gas:
2H⁺ + 2e⁻ → H₂
Sodium ions are not reduced because sodium is more reactive than hydrogen; the reduction potential for Na⁺/Na is more negative than that for H⁺/H₂, so hydrogen ions are discharged preferentially.