Match List I with List II
| List I | List II |
| (A) Fuel cell | (I) Rechargeable |
| (B) Mercury cell | (II) Reaction at anode, \(Zn \longrightarrow Zn^{2+} + 2e^-\) |
| (C) Leclanche cell | (III) Cell reaction, \(2H_2 + O_2 \longrightarrow 2H_2O\) |
| (D) Ni-Cd cell | (IV) Gives steady potential |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A)-(III), (B)-(IV), (C)-(II), (D)-(I)
Each cell is identified by its reactions or its key property: primary cells (Leclanche, mercury) cannot be recharged, secondary cells (nickel–cadmium, lead storage) can, and a fuel cell runs on a continuous supply of reactants.
(A) Fuel cell — This matches (III) Cell reaction, \(2H_2 + O_2 \longrightarrow 2H_2O\). In the \( \ce{H2-O2} \) fuel cell the gases are bubbled through porous carbon electrodes into aqueous NaOH:
Cathode: \( \ce{O2(g) + 2H2O(l) + 4e- -> 4OH^-(aq)} \); Anode: \( \ce{2H2(g) + 4OH^-(aq) -> 4H2O(l) + 4e-} \)
(B) Mercury cell — This matches (IV) Gives steady potential. Its cell reaction involves no ion whose concentration changes, so the cell potential stays constant (about 1.35 V) during its life:
\( \ce{Zn(Hg) + HgO(s) -> ZnO(s) + Hg(l)} \)
(C) Leclanche cell — This matches (II) Reaction at anode, \(Zn \longrightarrow Zn^{2+} + 2e^-\). In the dry cell the zinc container is the anode; \( \ce{MnO2} \) with carbon is the cathode:
Anode: \( \ce{Zn(s) -> Zn^2+ + 2e-} \); Cathode: \( \ce{MnO2 + NH4+ + e- -> MnO(OH) + NH3} \)
(D) Ni-Cd cell — This matches (I) Rechargeable. The nickel–cadmium cell is a secondary cell with a longer life than the lead storage cell:
\( \ce{Cd(s) + 2Ni(OH)3(s) -> CdO(s) + 2Ni(OH)2(s) + H2O(l)} \)
Shortcut: (A)-(III) appears only in Option (3).