Match List-I with List-II.
| List-I | List-II |
| (A) Leclanché cell (dry cell) | (p) Overall cell reaction: 2H2 + O2 → 2H2O |
| (B) Nickel-cadmium cell | (q) Overall reaction involves no ion in solution; used in hearing aids |
| (C) Fuel cell | (r) Secondary cell that can be recharged |
| (D) Mercury cell | (s) Anode reaction: Zn(s) → Zn2+ + 2e− |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → A-s, B-r, C-p, D-q
(A) Leclanché cell (dry cell) — This matches (s) Anode reaction: Zn(s) → Zn2+ + 2e−. The zinc container is the anode, where zinc is oxidised:
Anode: \( \displaystyle \ce{Zn(s) -> Zn^2+ + 2e^-} \)
(B) Nickel-cadmium cell — This matches (r) Secondary cell that can be recharged. It is a secondary cell, with a longer life than the lead storage cell.
(C) Fuel cell — This matches (p) Overall cell reaction: 2H2 + O2 → 2H2O. In the hydrogen–oxygen fuel cell the gases are bubbled through porous carbon electrodes into concentrated NaOH:
Cathode: \( \displaystyle \ce{O2(g) + 2H2O(l) + 4e^- -> 4OH^-(aq)} \)
Anode: \( \displaystyle \ce{2H2(g) + 4OH^-(aq) -> 4H2O(l) + 4e^-} \)
Cell reaction: \( \displaystyle \ce{2H2(g) + O2(g) -> 2H2O(l)} \)
(D) Mercury cell — This matches (q) Overall reaction involves no ion in solution; used in hearing aids. The anode is zinc–mercury amalgam and the cathode a paste of HgO and carbon:
Cell reaction: \( \displaystyle \ce{Zn(Hg) + HgO(s) -> ZnO(s) + Hg(l)} \)
No ion in solution changes in concentration, so the potential stays at about 1.35 V; this suits low current devices like hearing aids.
NCERT (2026-27 edition):
2.6.1 Primary Batteries – “… The cell consists of a zinc container that also acts as anode and the cathode is a carbon (graphite) rod surrounded by powdered manganese dioxide and carbon …”
“Mercury cell, … suitable for low current devices like hearing aids, watches, etc. consists of zinc – mercury amalgam as anode and a paste of HgO and carbon as the cathode. … The cell potential is approximately 1.35 V and remains constant during its life as the overall reaction does not involve any ion in solution whose concentration can change during its life time.”
2.6.2 Secondary Batteries – “A secondary cell after use can be recharged by passing current through it in the opposite direction so that it can be used again. … Another important secondary cell is the nickel-cadmium cell … which has longer life than the lead storage cell but more expensive to manufacture.”
2.7 Fuel Cells – “One of the most successful fuel cells uses the reaction of hydrogen with oxygen to form water …”