Which cell is rechargeable?

Nickle-cadmium cell

The correct answer is Option (1) → Nickle-cadmium cell

Electrochemical cells are broadly classified into two main types based on their ability to be recharged:

1. Primary Cells (Non-rechargeable):
• The reaction proceeds only in one direction, and once the reactants are consumed, the cell cannot be reused.
• Examples: Dry cell (Leclanché cell), Mercury cell, Daniell cell.
2. Secondary Cells (Rechargeable):
• The chemical reaction can be reversed by passing an external electric current through the cell (charging). This regenerates the original reactants.
• Examples: Nickel-cadmium ($\text{NiCd}$) cell, Lead storage battery (Lead-acid battery), Lithium-ion battery.

Nickel-Cadmium Cell ($\text{NiCd}$)

• The $\text{NiCd}$ cell is a type of secondary cell.
• The overall reaction during discharge is:

$\text{Cd}(s) + 2\text{Ni}(\text{OH})_3(s) \overset{\text{Discharge}}{\longrightarrow} \text{Cd}(\text{OH})_2(s) + 2\text{Ni}(\text{OH})_2(s)$

• By applying an external voltage greater than the cell potential, the reaction can be reversed (charging), making the cell fully reusable.
• Used in rechargeable batteries, cameras, emergency lights, cordless phones, etc.

Daniell Cell

• It is a primary cell.

• Once the chemicals are used up, the reaction cannot be reversed easily.

• Not rechargeable.

Mercury Cell

• Also a primary cell.

• Gives constant voltage and long life but cannot be recharged.

• Common in watches and hearing aids.

Dry Cell

• A primary cell.

• Used in torches, remotes, toys.

• Chemicals get exhausted and cannot be recharged.