Which of the following species participate in sulphonation of benzene ring ?

Options

A. `H_(2)SO_(4)`
B. `SO_(3)`
C. `HSO_(3)^(-)`
D. `SO_(2)^(-)`

Explanation

To solve the question regarding which species participates in the sulfonation of the benzene ring, we will follow these steps:

### Step-by-Step Solution:

1. **Understanding Sulfonation of Benzene**:
- Sulfonation of benzene is an electrophilic substitution reaction where a sulfonyl group (–SO3H) is introduced into the benzene ring.

2. **Identifying the Reactants**:
- The primary reactant in this reaction is benzene (C6H6), which has a high electron density and can act as a nucleophile.

3. **Role of Sulfuric Acid**:
- Concentrated sulfuric acid (H2SO4) is typically used in this reaction. It can generate sulfur trioxide (SO3), which is the actual electrophile that reacts with benzene.

4. **Formation of Sulfur Trioxide**:
- The reaction of sulfuric acid can be represented as:
\[ 2 \text{H}_2\text{SO}_4 \rightarrow \text{SO}_3 + \text{H}_2\text{O} + \text{HSO}_4^- \]
- Here, sulfur trioxide (SO3) is formed, which is crucial for the sulfonation process.

5. **Electrophilic Attack**:
- The sulfur trioxide (SO3) has a partial positive charge on sulfur due to the electronegativity of oxygen, making it a strong electrophile.
- Benzene donates its electron density to the sulfur, leading to the formation of a sigma complex (an arenium ion).

6. **Formation of Benzene Sulfonic Acid**:
- The intermediate formed loses a proton (H+) to regenerate the aromatic system, resulting in the formation of benzene sulfonic acid (C6H5SO3H).

7. **Conclusion**:
- From the above steps, we can conclude that the species that participates in the sulfonation of benzene is sulfur trioxide (SO3).

### Final Answer:
- The species that participates in the sulfonation of the benzene ring is **sulfur trioxide (SO3)**, which corresponds to **option 2**.