Match List-I with List-II.List-IList-II(i) Lead storage battery(a) Hi…

The correct answer is Option (4) → i-d, ii-c, iii-a, iv-b

All four items are electrochemical: three are cells that turn the energy of a chemical reaction into electrical energy, and rusting is an unwanted redox reaction on the surface of iron.

(i) Lead storage battery — This matches (d) Pb is the anode and PbO₂ is the cathode. It is a secondary cell with a lead anode, a lead grid packed with lead dioxide as cathode, and 38% sulphuric acid as electrolyte. On discharge:

    Anode: \( \displaystyle \ce{Pb(s) + SO4^2-(aq) -> PbSO4(s) + 2e^-} \)
    Cathode: \( \displaystyle \ce{PbO2(s) + SO4^2-(aq) + 4H^+(aq) + 2e^- -> PbSO4(s) + 2H2O(l)} \)
    Cell reaction: \( \displaystyle \ce{Pb(s) + PbO2(s) + 2H2SO4(aq) -> 2PbSO4(s) + 2H2O(l)} \)

(ii) Mercury cell — This matches (c) Cell potential remains constant during its life. The anode is zinc amalgam and the cathode a paste of HgO and carbon:

    Anode: \( \displaystyle \ce{Zn(Hg) + 2OH^- -> ZnO(s) + H2O + 2e^-} \)
    Cathode: \( \displaystyle \ce{HgO + H2O + 2e^- -> Hg(l) + 2OH^-} \)
    Cell reaction: \( \displaystyle \ce{Zn(Hg) + HgO(s) -> ZnO(s) + Hg(l)} \)

The cell reaction has no ion in solution whose concentration can change, so the potential stays at about 1.35 V.

(iii) Fuel cell — This matches (a) High efficiency of about 70%. The hydrogen–oxygen fuel cell turns the energy of combustion of hydrogen directly into electricity, with an efficiency of about 70%, against about 40% for thermal plants:

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

(iv) Rusting — This matches (b) Prevented by covering the surface with zinc. Rusting is an electrochemical process in which iron is oxidised:

    Anode: \( \displaystyle \ce{2Fe(s) -> 2Fe^2+ + 4e^-} \)
    Cathode: \( \displaystyle \ce{O2(g) + 4H^+(aq) + 4e^- -> 2H2O(l)} \)

A zinc coating keeps air and moisture away from the iron. Zinc is more easily oxidised than iron, so even where the coating is scratched, zinc corrodes first and saves the iron.

NCERT (2026-27 edition):
2.6.2 Secondary Batteries – “… The most important secondary cell is the lead storage battery … commonly used in automobiles and invertors. It consists of a lead anode and a grid of lead packed with lead dioxide (PbO₂) as cathode.”

2.6.1 Primary Batteries – “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.”

2.7 Fuel Cells – “… Fuel cells produce electricity with an efficiency of about 70 % compared to thermal plants whose efficiency is about 40%.”

2.8 Corrosion – “… Another simple method is to cover the surface by other metals (Sn, Zn, etc.) that are inert or react to save the object. An electrochemical method is to provide a sacrificial electrode of another metal (like Mg, Zn, etc.) which corrodes itself but saves the object.”