Which one of the following is the cathodic reaction in a fuel cell?

The correct answer is Option (2) → \(O_2 (g) + 2H_2O (l) + 4e^- \longrightarrow 4OH^- (aq)\)

In the \( \ce{H2-O2} \) fuel cell, hydrogen and oxygen are bubbled through porous carbon electrodes into concentrated aqueous NaOH. Reduction takes place at the cathode, and there oxygen is reduced to hydroxide ions:

    Cathode: \( \ce{O2(g) + 2H2O(l) + 4e- -> 4OH-(aq)} \)
    Anode: \( \ce{2H2(g) + 4OH-(aq) -> 4H2O(l) + 4e-} \)
    Cell reaction: \( \ce{2H2(g) + O2(g) -> 2H2O(l)} \)

• Option (1) \( \ce{2H2(g) + 4OH^-(aq) -> 4H2O(l) + 4e^-} \) — Incorrect. This is the anode reaction of the same fuel cell: hydrogen is oxidised and electrons are released.

• Option (3) \( \ce{PbO2(s) + SO4^2-(aq) + 4H^+(aq) + 2e^- -> PbSO4(s) + 2H2O(l)} \) — Incorrect. This is the cathode reaction of the lead storage battery during discharge, not of a fuel cell.

• Option (4) \( \ce{Pb(s) + SO4^2-(aq) -> PbSO4(s) + 2e^-} \) — Incorrect. This is the anode reaction of the lead storage battery: lead is oxidised to lead sulphate.

NCERT (2026-27 edition):
Fuel Cells – …