Question

Identify the change occuring in oxidation state of Mn in cell reaction of dry cell of clock during its use

• A. +3 → +4
• B. +2 → +7
• C. +4 → +3
• D. +7 → +2

Answer 1

The Correct Option is C

To determine the change in the oxidation state of Manganese (Mn) in the cell reaction of a dry cell used in clocks, consider the overall reaction involved in such cells. Commonly, dry cells like the Leclanché cell consist of a zinc anode and a cathode composed of a mixture of manganese dioxide (MnO₂), carbon, and an electrolyte.

The key reaction at the cathode is the reduction of manganese dioxide. Initially, manganese dioxide (MnO₂) is present with manganese in the +4 oxidation state. During the discharge of the cell, MnO₂ is reduced to manganese oxide (Mn₂O₃), where manganese is in the +3 oxidation state.

Thus, the oxidation half-reaction for manganese can be described as follows:

2 \text{MnO}_2 + 2 \text{NH}_4^+ + 2 \text{e}^- \rightarrow \text{Mn}_2\text{O}_3 + 2 \text{NH}_3 + \text{H}_2\text{O}

This shows that manganese undergoes a reduction process from +4 to +3 oxidation state.

Therefore, the correct change in the oxidation state of Mn in the cell reaction of a dry cell during its use is from +4 \rightarrow +3.

Let's evaluate the options:

• +3 → +4: This suggests an increase in oxidation state, which is incorrect as Mn is reduced.
• +2 → +7: There is no involvement of oxidation states +2 or +7 in this reaction.
• +4 → +3: This correctly describes the reduction of Mn from MnO₂ to Mn₂O₃.
• +7 → +2: No such transition occurs during the dry cell reaction.

The correct option is +4 → +3.