Which cell is rechargeable?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Nickel-cadmium cell
Commercial cells are of two kinds. In a primary cell the reaction takes place only once; after use the cell becomes dead and cannot be reused. A secondary cell can be recharged: passing current through it in the opposite direction reverses the cell reaction, so it can go through many charging and discharging cycles. The lead storage cell and the nickel-cadmium cell are secondary cells.
In the nickel-cadmium cell the reaction during discharge is:
\( \displaystyle \ce{Cd(s) + 2Ni(OH)3(s) -> CdO(s) + 2Ni(OH)2(s) + H2O(l)} \)
On charging, this reaction runs backwards and regenerates Cd and \( \ce{Ni(OH)3} \). The cell has a longer life than the lead storage cell, though it costs more to make. So the rechargeable cell is the nickel-cadmium cell.
Why the other options are incorrect
Option (2) Daniell cell — Incorrect. This Zn/Cu galvanic cell (about 1.1 V) is used to show how a cell works; it is not recharged in use.
Option (3) Mercury cell — Incorrect. It is a primary cell used in hearing aids and watches; its zinc anode is used up and it is discarded.
Option (4) Dry cell — Incorrect. The Leclanché dry cell is a primary cell used in torches and clocks; it cannot be recharged.
NCERT (2026-27 edition):
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.”