MHT CET202520 Apr 2025Evening ShiftChemistryElectrochemistryActual
Which of the following change takes place at positive electrode during working of dry cell?
Options
- AZn _ ( s ) is oxidised to Zn ⁺² _ ( aq )
- BZn ⁺² _ ( aq ) is reduced to Zn _ ( s )
- CMnO _ 2( ~s ) is reduced to Mn ₂ O _ 3( ~s )
- DMn ₂ O _ 3( ~s ) is oxidised to MnO _ 2( ~s )
Correct answer
C. MnO _ 2( ~s ) is reduced to Mn ₂ O _ 3( ~s )
Step-by-step solution
Dry Cell (Leclanché Cell) Reactions A dry cell uses zinc as the anode and a carbon rod surrounded by MnO₂ , carbon powder, and NH₄Cl as the cathode. At the anode (negative electrode), zinc undergoes oxidation: Zn _ (s) Zn ²⁺_ (aq) + 2 e ^- At the cathode (positive electrode), manganese dioxide is reduced: 2 MnO _ 2(s) + 2 NH ⁺_ 4(aq) + 2 e ^- Mn ₂ O _ 3(s) + 2 NH _ 3(aq) + H ₂ O _ (l) Manganese in MnO₂ has an oxidation state of +4, while in Mn₂O₃ it is +3. The decrease in oxidation number confirms reduction is occu