The products of the electrolysis of dilute sodium chloride using carbon electrodes are Anode Cathode

Analyze the question: We need the products at the anode and the cathode when dilute sodium chloride solution is electrolysed using inert carbon electrodes. The order matters: anode first, then cathode.

Concept: Selective (preferential) discharge

The ions in the solution are:

• From NaCl: Na⁺ and Cl⁻
• From water: H⁺ and OH⁻

At the cathode (negative electrode), cations compete. H⁺ is lower than Na⁺ in the electrochemical series, so H⁺ is discharged: 2H⁺ + 2e⁻ → H₂

At the anode (positive electrode), anions compete. Three factors matter:

• Position in the electrochemical series: OH⁻ is preferred over Cl⁻.
• Concentration: in a concentrated NaCl solution, the high concentration of Cl⁻ overrides this and chlorine is discharged. In a dilute solution, there is little Cl⁻, so OH⁻ is discharged.
• Electrode: carbon is inert, so it does not react.

Anode reaction in dilute solution: 4OH⁻ → 2H₂O + O₂ + 4e⁻

Products:

• Anode: oxygen
• Cathode: hydrogen

Checking the options:

• A. Chlorine and sodium: sodium is never discharged from aqueous solution. Wrong.
• B. Oxygen (anode) and hydrogen (cathode): matches. Correct.
• C. Chlorine and hydrogen: this is for concentrated brine. Wrong.
• D. Hydrogen and oxygen: the electrodes are reversed. Wrong.

Answer: B

Exam tip: Always check the word "dilute" or "concentrated" in electrolysis questions.

• Concentrated NaCl gives Cl₂ at the anode and H₂ at the cathode.
• Dilute NaCl gives O₂ at the anode and H₂ at the cathode.

Also remember "Anode = Anions (negative ions) go there, and Oxidation happens there" (AN OX), and read the order "Anode, Cathode" carefully in the options.