Nitration of benzene by nitric acid and sulphuric acid is

Options

A. electrophilic substitution
B. electrophilic addition
C. nucleophilic substitution
D. free radical substitution.

Answer

To solve the question regarding the nitration of benzene by nitric acid and sulfuric acid, we will break down the process step by step.

### Step-by-Step Solution:

1. **Understanding the Reactants**:
- The reaction involves benzene (C6H6), concentrated nitric acid (HNO3), and concentrated sulfuric acid (H2SO4).
- The purpose of sulfuric acid is to act as a catalyst in the reaction.

**Hint**: Identify the reactants involved in the nitration process.

2. **Formation of the Electrophile**:
- When concentrated sulfuric acid is mixed with concentrated nitric acid, it generates the nitronium ion (NO2+), which is a strong electrophile.
- The reaction can be summarized as:
\[ H2SO4 + HNO3 \rightarrow HSO4^- + NO2^+ + H2O \]

**Hint**: Recognize that the nitronium ion is the key electrophile in this reaction.

3. **Electrophilic Attack on Benzene**:
- The benzene ring is electron-rich due to its delocalized pi electrons. The nitronium ion (NO2+) attacks the benzene ring, forming a sigma complex (also known as an arenium ion).
- This step can be represented as:
\[ C6H6 + NO2^+ \rightarrow C6H5NO2^+ (sigma complex) \]

**Hint**: Understand that the electrophile attacks the electron-rich benzene ring.

4. **Rearrangement and Deprotonation**:
- The sigma complex is unstable and undergoes rearrangement. A hydrogen atom from the benzene ring is removed (deprotonation), restoring the aromaticity of the ring.
- This results in the formation of nitrobenzene (C6H5NO2) and a proton (H+).
- The overall reaction can be summarized as:
\[ C6H5NO2^+ \rightarrow C6H5NO2 + H^+ \]

**Hint**: Remember that the aromaticity of benzene is restored after the electrophilic substitution.

5. **Final Product**:
- The final product of the nitration of benzene is nitrobenzene (C6H5NO2).

**Hint**: Identify the final product formed after the reaction.

### Conclusion:
The nitration of benzene by nitric acid and sulfuric acid is an example of **electrophilic substitution**. The nitronium ion acts as the electrophile that substitutes a hydrogen atom on the benzene ring, resulting in the formation of nitrobenzene.

### Final Answer:
The correct answer to the question is **electrophilic substitution**.