\(Zn(s) \longrightarrow Zn^{2+} + 2e^-\)
Above reaction at anode is found in :
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Leclanche cell
In the Leclanche cell (dry cell) the zinc container itself is the anode, and the anode reaction is the oxidation of zinc to \( \ce{Zn^{2+}} \) ions:
Anode: Zn(s) → \( \ce{Zn^{2+}} \) + 2e−
Cathode: \( \ce{MnO2} \) + \( \ce{NH4^{+}} \) + e− → MnO(OH) + \( \ce{NH3} \)
Why the other options are incorrect
Option (2) Mercury cell — Incorrect. The anode is zinc–mercury amalgam in alkaline paste, and zinc ends up as ZnO: Zn(Hg) + \( \ce{2OH^{-}} \) → ZnO(s) + \( \ce{H2O} \) + 2e−, not free \( \ce{Zn^{2+}} \).
Option (3) Ni-Cd cell — Incorrect. The anode is cadmium, not zinc.
Option (4) Fuel cell — Incorrect. In the \( \ce{H2-O2} \) fuel cell the anode reaction is the oxidation of hydrogen: \( \ce{2H2} \) + \( \ce{4OH^{-}} \) → \( \ce{4H2O} \) + 4e−.
NCERT (2026-27 edition):
Primary Batteries – “… The most familiar example of this type is the dry cell (known as Leclanche cell after its discoverer) which is used commonly in our transistors and clocks. 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 …”