When `MnO_2` is strongly heated to get oxygen gas, the oxidation number of Mn changes from + 4 to ?

Options

A. 0
B. `+1`
C. `+8/3`
D. `+2`

Answer

To solve the question regarding the change in the oxidation number of manganese (Mn) when `MnO2` is strongly heated to produce oxygen gas, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Initial Oxidation State of Mn in MnO2**:
- In `MnO2`, manganese (Mn) is combined with two oxygen atoms. The oxidation state of oxygen is typically -2.
- To find the oxidation state of Mn, we can set up the equation:
\[ x + 2(-2) = 0 \]
where \( x \) is the oxidation state of Mn.
- Solving this gives:
\[ x - 4 = 0 \implies x = +4 \]
- Therefore, the oxidation state of Mn in `MnO2` is +4.

2. **Understand the Reaction When MnO2 is Heated**:
- When `MnO2` is heated, it decomposes to release oxygen gas (O2) and forms manganese sulfate (MnSO4) in the presence of an acidic medium (like H2SO4).
- The balanced reaction can be represented as:
\[ 2MnO2 + 2H2SO4 \rightarrow 2MnSO4 + 2H2O + O2 \]

3. **Identify the Final Oxidation State of Mn in MnSO4**:
- In `MnSO4`, we need to determine the oxidation state of Mn again.
- The sulfate ion (SO4) has an oxidation state of -2. Thus, we can set up the equation:
\[ x + (-2) = 0 \]
where \( x \) is the oxidation state of Mn in `MnSO4`.
- Solving this gives:
\[ x - 2 = 0 \implies x = +2 \]
- Therefore, the oxidation state of Mn in `MnSO4` is +2.

4. **Determine the Change in Oxidation State**:
- The oxidation state of Mn changes from +4 in `MnO2` to +2 in `MnSO4`.
- Thus, the change in oxidation number is from +4 to +2.

### Conclusion:
The oxidation number of Mn changes from +4 to +2 when `MnO2` is strongly heated to produce oxygen gas.