Match List-I with List-II
| List-I | List-II |
| Process/ Cell/Battery | Characteristics |
| (A) Lead Storage Battery | (I) H2 and O2 are used. |
| (B) Mercury cell | (II) Tarnishing of silver. |
| (C) Fuel Cell | (III) Used in low current devices. |
| (D) Corrosion | (IV) Anode and cathode are made up of Pb and PbO2 respectively. |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (A) - (IV), (B) - (III), (C) - (I), (D) - (II)
Batteries and fuel cells turn the chemical energy of a redox reaction into electrical energy. Corrosion is the same kind of electrochemical process happening unwanted on a metal surface. Each item is recognised by its electrodes, reactants or use:
(A) Lead Storage Battery — This matches (IV) Anode and cathode are made up of Pb and PbO2 respectively. It is a secondary (rechargeable) cell used in automobiles, with a lead anode, a lead dioxide cathode and about 38% sulphuric acid as electrolyte.
\( \displaystyle \text{Anode: }\ce{Pb(s) + SO4^2-(aq) -> PbSO4(s) + 2e^-} \)
\( \displaystyle \text{Cathode: }\ce{PbO2(s) + SO4^2-(aq) + 4H^+(aq) + 2e^- -> PbSO4(s) + 2H2O(l)} \)
\( \displaystyle \text{Cell reaction: }\ce{Pb(s) + PbO2(s) + 2H2SO4(aq) -> 2PbSO4(s) + 2H2O(l)} \)
(B) Mercury cell — This matches (III) Used in low current devices. It gives a steady 1.35 V over its life and is used in hearing aids and watches.
\( \displaystyle \text{Anode: }\ce{Zn(Hg) + 2OH^- -> ZnO(s) + H2O + 2e^-} \)
\( \displaystyle \text{Cathode: }\ce{HgO(s) + H2O + 2e^- -> Hg(l) + 2OH^-} \)
\( \displaystyle \text{Cell reaction: }\ce{Zn(Hg) + HgO(s) -> ZnO(s) + Hg(l)} \)
(C) Fuel Cell — This matches (I) H2 and O2 are used. Hydrogen and oxygen are bubbled continuously through porous carbon electrodes into an electrolyte, and the energy of their combustion is obtained as electricity.
\( \displaystyle \text{Cathode: }\ce{O2(g) + 2H2O(l) + 4e^- -> 4OH^-(aq)} \)
\( \displaystyle \text{Anode: }\ce{2H2(g) + 4OH^-(aq) -> 4H2O(l) + 4e^-} \)
\( \displaystyle \text{Cell reaction: }\ce{2H2(g) + O2(g) -> 2H2O(l)} \)
(D) Corrosion — This matches (II) Tarnishing of silver. In corrosion, the surface of a metal is slowly converted into its oxide, sulphide or carbonate by air and moisture. Tarnishing of silver (a black \( \ce{Ag2S} \) layer), rusting of iron and the green coating on copper are examples. Silver tarnishes in air containing traces of hydrogen sulphide:
\( \displaystyle \ce{4Ag + 2H2S + O2 -> 2Ag2S + 2H2O} \)
Shortcut: The pair (A)–(IV) appears only in Option (4).