Which of the following acts as a self-indicator ?

Options

A. `K_(2)Cr_(2)O_(7)`
B. `KMnO_(4)`
C. `Oxalic acid`
D. Iodine

Explanation

To determine which of the following substances acts as a self-indicator, we need to understand the concept of indicators in titration and specifically what a self-indicator is.

### Step-by-Step Solution:

1. **Understanding Indicators**: Indicators are substances that change color at a specific pH level. They are used in titrations to signal the endpoint of the reaction.

2. **Definition of Self-Indicator**: A self-indicator is a substance that does not require an external indicator to indicate the endpoint of a titration. It changes color on its own during the reaction.

3. **Analyzing KMnO4**: Potassium permanganate (KMnO4) is a common titrant in redox reactions. It is a purple-colored solution. During a titration, as it reacts, it changes from purple to a light pink color when it reaches the endpoint. This color change occurs due to the reduction of MnO4^- ions to Mn^2+ ions.

4. **Conclusion about KMnO4**: Since KMnO4 changes color by itself during the titration process, it qualifies as a self-indicator. There is no need for an additional indicator to determine the endpoint.

5. **Comparing with Other Substances**: Other substances like methyl orange and phenolphthalein require an external indicator to show a color change at specific pH levels. Therefore, they are not self-indicators.

6. **Final Answer**: The substance that acts as a self-indicator is KMnO4.