The pink colour of phenolphthalein in alkaline medium is due to

Options

A. `overset(Theta)OH` ions
B. Positive ion
C. Negative ion
D. Neutral form

Explanation

To solve the question regarding the pink color of phenolphthalein in alkaline medium, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Phenolphthalein**:
- Phenolphthalein is an organic compound that acts as a pH indicator. It is colorless in acidic solutions and turns pink in alkaline solutions.

**Hint**: Remember that phenolphthalein changes color based on the pH of the solution.

2. **Acidic Nature of Phenolphthalein**:
- Phenolphthalein has an acidic hydrogen atom in its structure. This hydrogen is responsible for its acidic properties.

**Hint**: Identify the acidic hydrogen in the structure of phenolphthalein.

3. **Reaction with Alkaline Medium**:
- When phenolphthalein is added to an alkaline solution, the hydroxide ions (OH⁻) in the solution react with the acidic hydrogen (H⁺) of phenolphthalein. This reaction neutralizes the acidic hydrogen.

**Hint**: Consider what happens to the acidic hydrogen when it encounters a base.

4. **Formation of the Phenolphthalein Anion**:
- After the neutralization of the acidic hydrogen, what remains is the phenolphthalein anion (P⁻). This anion is responsible for the pink color observed in alkaline solutions.

**Hint**: Focus on the species that remains after the acidic hydrogen is neutralized.

5. **Conclusion**:
- The pink color of phenolphthalein in alkaline medium is due to the presence of the phenolphthalein anion (P⁻), which has resonance stabilization and imparts the pink color.

**Hint**: Remember that the color change is due to the formation of a specific ion in the solution.

### Final Answer:
The pink color of phenolphthalein in alkaline medium is due to the presence of the **negative ion (P⁻)** formed after the neutralization of the acidic hydrogen.