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 determine 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**:
- In `MnO2`, manganese (Mn) has an oxidation state of +4. This is because each oxygen atom has an oxidation state of -2, and there are two oxygen atoms. Therefore, the equation for the oxidation state can be set up as:
\[ x + 2(-2) = 0 \quad \text{(where x is the oxidation state of Mn)} \]
Solving this gives:
\[ x - 4 = 0 \implies x = +4 \]

2. **Understand the Reaction**:
- When `MnO2` is heated, it decomposes to release oxygen gas. The reaction can be represented as:
\[ 2 \text{MnO}_2 \rightarrow 2 \text{MnSO}_4 + \text{O}_2 + 2 \text{H}_2O \]
- In this reaction, manganese is being reduced.

3. **Determine the Final Oxidation State**:
- In the product `MnSO4`, the oxidation state of manganese can be calculated similarly. In `MnSO4`, the sulfate ion (SO4) has a charge of -2. Therefore, the oxidation state of Mn can be calculated as:
\[ x + (-2) = 0 \quad \text{(where x is the oxidation state of Mn in MnSO4)} \]
Solving this gives:
\[ x - 2 = 0 \implies x = +2 \]

4. **Calculate the Change in Oxidation State**:
- The change in oxidation state of Mn from `MnO2` to `MnSO4` is:
\[ +4 \text{ (in MnO2)} \rightarrow +2 \text{ (in MnSO4)} \]
- Thus, the oxidation number of Mn changes from +4 to +2.

### Final Answer:
The oxidation number of Mn changes from +4 to +2.