Aromatic electrophilic substitution reaction that is reversible is

Options

A. nitration
B. chlorination
C. sulphonation
D. alkylation

Explanation

To solve the question regarding which aromatic electrophilic substitution reaction is reversible, we will analyze the process of sulfonation of benzene.

### Step-by-Step Solution:

1. **Understanding Aromatic Electrophilic Substitution**:
- Aromatic compounds undergo electrophilic substitution reactions where an electrophile replaces a hydrogen atom on the aromatic ring.

2. **Identifying the Reaction**:
- The question asks for a specific aromatic electrophilic substitution reaction that is reversible. One well-known reaction is the sulfonation of benzene.

3. **Sulfonation Reaction**:
- The sulfonation of benzene involves the introduction of a sulfonyl group (-SO3H) into the benzene ring. This is typically achieved by treating benzene with concentrated sulfuric acid (H2SO4) or sulfur trioxide (SO3).

4. **Reaction Representation**:
- The reaction can be represented as follows:
\[ \text{C}_6\text{H}_6 + \text{SO}_3 \rightarrow \text{C}_6\text{H}_5\text{SO}_3\text{H} \]
- Here, benzene (C6H6) reacts with sulfur trioxide (SO3) to form benzene sulfonic acid (C6H5SO3H).

5. **Reversibility of the Reaction**:
- The sulfonation reaction is reversible. Benzene sulfonic acid can be converted back to benzene and sulfur trioxide under certain conditions, such as heating with water:
\[ \text{C}_6\text{H}_5\text{SO}_3\text{H} + \text{H}_2\text{O} \rightleftharpoons \text{C}_6\text{H}_6 + \text{H}_2\text{SO}_4 \]

6. **Conclusion**:
- Therefore, the aromatic electrophilic substitution reaction that is reversible is **sulfonation**.

### Final Answer:
The reversible aromatic electrophilic substitution reaction is **sulfonation**.

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