Sulphonation of benzene is done by which reagent?

Options

A. Conc. `HNO_3 + Conc. H_2SO_4`
B. Fuming sulphuric acid
C. `SO_2`
D. Dilute sulphuric acid

Answer

To determine the reagent used for the sulphonation of benzene, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Process of Sulphonation**:
- Sulphonation is a chemical reaction where a sulfonyl group (–SO3H) is introduced into an aromatic compound, in this case, benzene.

2. **Identify the Product**:
- The product of the sulphonation of benzene is benzene sulfonic acid (C6H5SO3H).

3. **Determine the Reagent**:
- The common reagent used for the sulphonation of benzene is fuming sulfuric acid (H2SO4). This is concentrated sulfuric acid that contains sulfur trioxide (SO3) dissolved in it.

4. **Reaction Overview**:
- When benzene reacts with fuming sulfuric acid, the sulfur trioxide (SO3) reacts with benzene to form benzene sulfonic acid.

5. **Conclusion**:
- Therefore, the reagent used for the sulphonation of benzene is fuming sulfuric acid (H2SO4).

### Final Answer:
The reagent used for the sulphonation of benzene is fuming sulfuric acid (H2SO4).

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