Concept:In the electrolysis of aqueous solutions, competition occurs at the electrodes between the ions from the salt and the water molecules themselves.
Solution:- In a dilute aqueous solution of NaCl, the concentration of \( Cl^- \) ions is very low compared to water molecules.
- At the anode (where oxidation occurs), two reactions compete: the oxidation of \( Cl^- \) to \( Cl_2 \) gas, and the oxidation of \( H_2O \) (or \( OH^- \)) to \( O_2 \) gas.
- Thermodynamically, the oxidation of water (requiring \( +1.23 \text{ V} \)) is easier than the oxidation of chloride ions (requiring \( +1.36 \text{ V} \)).
- Because the solution is dilute, the overpotential effect that usually favors Chlorine gas in concentrated brine is negligible. Thus, Oxygen gas is evolved at the anode.
Why other options are incorrect:Chlorine gas is only evolved if the NaCl solution is highly concentrated (brine). Hydrogen is evolved at the cathode, not the anode.
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