Read the following passage given below and answer the question.
Production of electricity by thermal plants is not very efficient method. It is now possible to make cells in which reactants are fed continuously to the electrodes and products are also removed continuously. One of the most successful fuel cells is hydrogen fuel cell.
In hydrogen fuel cell, the reactants are bubbled through which electrodes?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Porous carbon electrodes
A fuel cell is a galvanic cell in which the reactants are fed in continuously. In the \( \ce{H2-O2} \) fuel cell, hydrogen and oxygen are bubbled through porous carbon electrodes into concentrated aqueous NaOH. The porous carbon lets the gases reach the electrolyte, and finely divided Pt or Pd is built into the electrodes as a catalyst. The electrode reactions are:
\( \displaystyle \text{Anode: }\ce{2H2(g) + 4OH^-(aq) -> 4H2O(l) + 4e^-} \)
\( \displaystyle \text{Cathode: }\ce{O2(g) + 2H2O(l) + 4e^- -> 4OH^-(aq)} \)
\( \displaystyle \text{Cell reaction: }\ce{2H2(g) + O2(g) -> 2H2O(l)} \)
Option (1) Saturated calomel electrode — Incorrect. It is a reference electrode (Hg/\( \ce{Hg2Cl2} \)) used to measure electrode potentials, not a gas electrode of a fuel cell.
Option (2) Silver electrodes — Incorrect. Solid silver plates are not used; the gases need a porous electrode to reach the electrolyte.
Option (3) Platinum electrodes — Incorrect. Platinum is only the finely divided catalyst incorporated into the carbon electrodes; the gases are not bubbled through platinum electrodes.
NCERT (2026-27 edition):
Fuel Cells – “… In the cell, hydrogen and oxygen are bubbled through porous carbon electrodes into concentrated aqueous sodium hydroxide solution. Catalysts like finely divided platinum or palladium metal are incorporated into the electrodes for increasing the rate of electrode reactions.”