`MnO_4^-2` undergoes disproportionation reaction in acidic medium but `MnO_4^-`does not because

Options

A. In `MnO_4^-2`,Mn is in intermediate oxidation state
B. In `MnO_4^-2`,Mn is in lowest oxidation state
C. In `MnO_4^-2` ,Mn is in intermediate oxidation state
D. none of the above

Answer

To understand why `MnO4^-2` undergoes disproportionation in acidic medium while `MnO4^-` does not, we need to analyze the oxidation states of manganese in both species and the nature of disproportionation reactions.

### Step-by-Step Solution:

1. **Define Disproportionation Reaction**:
A disproportionation reaction is a specific type of redox reaction where a single substance is simultaneously oxidized and reduced, resulting in two different products.

2. **Identify the Oxidation States**:
- For `MnO4^-2`, we need to determine the oxidation state of manganese (Mn).
- Let the oxidation state of Mn be \( x \).
- The equation for the oxidation state is:
\[ x + 4(-2) = -2 \quad \text{(since there are 4 oxygen atoms, each with an oxidation state of -2)} \]
\[ x - 8 = -2 \implies x = +6 \]
- For `MnO4^-`, we perform a similar calculation:
\[ x + 4(-2) = -1 \]
\[ x - 8 = -1 \implies x = +7 \]

3. **Analyze the Ability to Disproportionate**:
- In `MnO4^-2` (Mn in +6 oxidation state), manganese can be oxidized to +7 and reduced to +4 or +2. This allows for both oxidation and reduction to occur, making it capable of disproportionation.
- In `MnO4^-` (Mn in +7 oxidation state), manganese can only be reduced (to +6 or +4) but cannot be oxidized further (since it is already at the highest oxidation state of +7). Therefore, it cannot undergo disproportionation.

4. **Conclusion**:
The ability of `MnO4^-2` to undergo disproportionation in acidic medium is due to the presence of manganese in the +6 oxidation state, allowing it to both gain and lose electrons. In contrast, `MnO4^-` cannot undergo this reaction because manganese is already in the +7 oxidation state, which limits its ability to participate in both oxidation and reduction.

### Final Answer:
`MnO4^-2` undergoes disproportionation in acidic medium because manganese is in the +6 oxidation state, allowing it to be both oxidized and reduced. In contrast, `MnO4^-` cannot disproportionate as manganese is in the +7 oxidation state, which only allows for reduction.