The figure shows a commercial dry cell.While the cell is in use, the…

The correct answer is Option (2) → From +4 to +3

The figure labels the carbon rod as the cathode and shows it surrounded by a paste of MnO₂, carbon black and NH₄Cl. Reduction takes place at the cathode, so manganese is reduced:

    Cathode: \( \ce{MnO2 + NH4^+ + e^- -> MnO(OH) + NH3} \)

Oxidation state of Mn in MnO₂: x + 2(–2) = 0, so x = +4.

Oxidation state of Mn in MnO(OH): x + (–2) + (–1) = 0, so x = +3.

Each MnO₂ takes up one electron, and manganese changes from +4 to +3.

NCERT (2026-27 edition):
2.6.1 Primary Batteries – “…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 (Fig.2.8). The space between the electrodes is filled by a moist paste of ammonium chloride (NH₄Cl) and zinc chloride (ZnCl₂). The electrode reactions are complex, but they can be written approximately as follows :”

    Anode: Zn(s) → Zn²⁺ + 2e^–

    Cathode: MnO₂ + NH₄⁺ + e^– → MnO(OH) + NH₃

“In the reaction at cathode, manganese is reduced from the + 4 oxidation state to the +3 state.”

Fig. 2.8: A commercial dry cell consists of a graphite (carbon) cathode in a zinc container; the latter acts as the anode.