The colour change of an indicator Hln in acid base titrations is given below
`underset("Colour x")(Hln(aq))hArr H+(aq)+ln^(-)underset("Colour Y")((aq))`
Which of the following statements is correct?

Options

A. In a strong alkaline solution colour Y will be obwerved
B. In a strong acidic solution colour Y will be observed
C. Concentration of `ln^(-)` is higher than that of Hln at the equivalence point
D. In a strong alkaline solution colour X is observed

Answer

To solve the question regarding the color change of the indicator HIn in acid-base titrations, we need to analyze the equilibrium reaction provided:

\[ \text{HIn (aq)} \rightleftharpoons \text{H}^+ (aq) + \text{In}^- (aq) \]

### Step-by-Step Solution:

1. **Identify the Forms of the Indicator:**
- The indicator HIn has two forms: the undissociated form (HIn) and the dissociated form (In^-).
- The color of the undissociated form (HIn) is represented as Color X.
- The color of the dissociated form (In^-) is represented as Color Y.

2. **Understand the Color Change:**
- In acidic solutions, the concentration of H^+ ions is high, which favors the formation of HIn (Color X).
- In basic solutions, the concentration of H^+ ions decreases, favoring the formation of In^- (Color Y).

3. **Determine the pH Ranges for Color Visibility:**
- For the color of the dissociated form (In^-) to be visible, the concentration of In^- must be at least 10 times that of H^+ ions. This corresponds to a pH value that is higher than the pKa of the indicator.
- Conversely, for the color of the undissociated form (HIn) to be visible, the concentration of HIn must be at least 10 times that of In^-. This corresponds to a pH value that is lower than the pKa of the indicator.

4. **Analyze the Given Statements:**
- **Statement 1:** In strong alkaline solution, Color Y will be observed.
- This is correct because in a strong alkaline solution, the pH is high, favoring the dissociated form (In^-) and thus Color Y.
- **Statement 2:** In strong acidic medium solution, Color Y will be observed.
- This is incorrect. In a strong acidic medium, the pH is low, favoring the undissociated form (HIn) and thus Color X.
- **Statement 3:** At the equivalence point, the colors of HIn and In^- will be the same.
- This is correct as at the equivalence point, the concentrations of HIn and In^- will be equal.

5. **Conclusion:**
- The correct statement regarding the indicator HIn is that in strong alkaline solutions, Color Y will be observed.

### Final Answer:
The correct statement is: **In strong alkaline solution, Color Y will be observed.**

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