Phenol + Phthalic anhydride `overset("Conc."H_(2)SO_(4))underset("fusion")(to)B`. B gives which of following colour in alkaline medium.

Options

A. Yellow
B. Colourless
C. Pink
D. Violet

Answer

To solve the question regarding the reaction of phenol with phthalic anhydride and the color produced in an alkaline medium, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Reactants**: The reactants in this reaction are phenol (C6H5OH) and phthalic anhydride (C8H4O3).

2. **Understand the Reaction Conditions**: The reaction is carried out in the presence of concentrated sulfuric acid (H2SO4) and involves fusion. This means that the reactants will undergo a condensation reaction, where water is eliminated.

3. **Reaction Mechanism**:
- When phenol reacts with phthalic anhydride, it can attack the carbonyl carbon of the anhydride.
- This leads to the formation of a compound where the phenol group is attached to the phthalic anhydride structure, resulting in the formation of phenolphthalein.

4. **Formation of Phenolphthalein**: The structure of phenolphthalein can be represented as follows:
- It has two phenolic groups linked to a phthalate structure, and it is known to be colorless in acidic conditions.

5. **Behavior in Alkaline Medium**:
- When phenolphthalein is placed in an alkaline medium (basic conditions), it undergoes a structural change that results in the compound exhibiting a pink color.
- This is due to the deprotonation of the phenolic hydroxyl groups, which increases the electron density and changes the light absorption properties of the compound.

6. **Conclusion**: Therefore, the compound B (phenolphthalein) will give a pink color in an alkaline medium.

### Final Answer:
The compound B gives a **pink color** in alkaline medium.