In the electrolysis of brine the anode is

Analyze the question: The question asks which material is used as the anode (positive electrode) when brine (concentrated sodium chloride solution) is electrolyzed.

Explain the concept: In the electrolysis of brine, the ions present are Na⁺, H⁺ (from water), Cl⁻ and OH⁻.

• At the anode (positive electrode), anions are discharged. Concentrated Cl⁻ is preferentially discharged over OH⁻: 2Cl⁻ → Cl₂ + 2e⁻
• At the cathode (negative electrode), H⁺ is discharged in preference to Na⁺: 2H⁺ + 2e⁻ → H₂

The anode must be inert, because chlorine gas is highly reactive. A reactive metal anode such as copper or zinc would dissolve or react with the chlorine and form metal chlorides instead of releasing Cl₂ gas.

Solution, option by option:

• A. Platinum: It is inert and would work. However, it is very expensive, so it is not the typical choice in standard school-level brine electrolysis.
• B. Copper: It is reactive. It would be oxidized (Cu → Cu²⁺ + 2e⁻) and react with chlorine, so it is unsuitable.
• C. Zinc: It is also reactive and would dissolve, so it is unsuitable.
• D. Carbon (graphite): It is inert, cheap and conducts electricity well. It resists chlorine, which makes it the standard anode for brine electrolysis. (In industry, titanium or graphite anodes are used in the diaphragm and mercury cells.)

carbon**.

Exam tip: Remember "Brine = Carbon anode." In JAMB questions, when the electrolyte is brine and the electrodes are not specified, carbon (graphite) is the usual answer. Platinum shows up mostly in dilute acid or water electrolysis questions, where it is used as an inert electrode.