Question

What happens in the oxidation number of Mn during working of dry cell.

• A. Increases by 1
• B. decreases by 1
• C. Increases by 2
• D. decreases by 2

Hint:

In the Leclanche dry cell manganese dioxide is reduced to Mn2O3.

Answer 1

The Correct Option is B

Step 1: Identify what is reduced:
Zinc loses electrons at the anode. The electrons travel to the cathode, where $\text{MnO}_2$ takes them.

Step 2: Count the change:
Mn in $\text{MnO}_2$ is $+4$. After taking one electron it becomes $+3$ in $\text{MnO(OH)}$ or $\text{Mn}_2\text{O}_3$.
A gain of one electron means the oxidation number falls by one. An increase would imply oxidation, which happens to zinc and not Mn.

Final Answer:
The oxidation number of Mn decreases by 1, option (B). \[ \boxed{\text{Decreases by } 1} \]