In acidic medium which of the following does not change its colour:

Options

A. `MnO_(4)^(-)`
B. `MnO_(4)^(2-)`
C. `CrO_(4)^(2-)`
D. `FeO_(4)^(2-)`

Explanation

To determine which of the given options does not change its color in acidic medium, we will analyze the behavior of each compound when subjected to acidic conditions.

### Step-by-Step Solution:

1. **Identify the Compounds**: The question provides several compounds, and we need to analyze their behavior in acidic medium. Let's denote the compounds as follows:
- A: MnO4^-
- B: MnO4^2-
- C: CrO4^2-
- D: FeO4^2-

2. **Analyze MnO4^- (Potassium Permanganate)**:
- In acidic medium, MnO4^- (purple color) reacts as follows:
\[ \text{MnO}_4^- + 8 \text{H}^+ + 5 \text{e}^- \rightarrow \text{Mn}^{2+} + 4 \text{H}_2\text{O} \]
- The product, Mn^2+, is colorless.
- **Conclusion**: MnO4^- changes from purple to colorless.

3. **Analyze MnO4^2- (Manganate Ion)**:
- In acidic medium, MnO4^2- reacts as follows:
\[ 2 \text{MnO}_4^{2-} + 2 \text{H}_2\text{O} \rightarrow 2 \text{MnO}_2 + 4 \text{OH}^- \]
- MnO4^2- is dark green and converts to MnO2 which is brown.
- **Conclusion**: MnO4^2- changes color.

4. **Analyze CrO4^2- (Chromate Ion)**:
- In acidic medium, CrO4^2- reacts as follows:
\[ 2 \text{CrO}_4^{2-} + 2 \text{H}^+ \rightarrow \text{Cr}_2\text{O}_7^{2-} + \text{H}_2\text{O} \]
- CrO4^2- is yellow and converts to Cr2O7^2- which is orange.
- **Conclusion**: CrO4^2- changes color.

5. **Analyze FeO4^2- (Ferrate Ion)**:
- In acidic medium, FeO4^2- reacts as follows:
\[ \text{FeO}_4^{2-} + 8 \text{H}^+ + 3 \text{e}^- \rightarrow \text{Fe}^{3+} + 4 \text{H}_2\text{O} \]
- FeO4^2- is typically unstable and can appear in various colors, often pink or yellow.
- **Conclusion**: FeO4^2- changes color.

### Final Conclusion:
Among the options analyzed, **MnO4^-** is the only compound that does not change its color in acidic medium as it transitions from a colored state (purple) to a colorless state (Mn^2+).

### Answer:
**Option A: MnO4^- does not change its color in acidic medium.**