In the nitration of an aromatic compound using a mixture of concentrated nitric acid and sulphuric acid, the acids respectively function as

Options

A. an oxidising agent and an acid
B. a Bronsted and a Lewis acid
C. a base and an acid
D. an acid and an oxidising agent

Answer

To solve the question regarding the function of concentrated nitric acid and sulfuric acid in the nitration of an aromatic compound, we can break down the process step by step.

### Step-by-Step Solution:

1. **Understanding the Reaction**:
- The nitration of aromatic compounds involves the introduction of a nitro group (-NO2) into the aromatic ring. This is typically achieved using a mixture of concentrated nitric acid (HNO3) and concentrated sulfuric acid (H2SO4).

2. **Role of Nitric Acid (HNO3)**:
- Nitric acid is a strong acid, but in this reaction, it acts as a base. This is because it accepts a proton (H+) from sulfuric acid. The reaction can be represented as:
\[ HNO3 + H2SO4 \rightleftharpoons H2NO3^+ + HSO4^- \]
- Here, the nitric acid accepts a proton, forming the nitronium ion (NO2^+) in the subsequent steps.

3. **Role of Sulfuric Acid (H2SO4)**:
- Sulfuric acid acts as a strong acid in this reaction. It donates a proton (H+) to nitric acid, facilitating the formation of the nitronium ion. The release of the proton characterizes sulfuric acid as an acid.

4. **Formation of the Nitronium Ion**:
- Following the proton transfer, the nitronium ion (NO2^+) is generated, which is the active electrophile that will attack the aromatic ring. The overall reaction can be summarized as:
\[ HNO3 + H2SO4 \rightarrow NO2^+ + H2O + HSO4^- \]

5. **Conclusion**:
- In summary, during the nitration process, nitric acid functions as a base (by accepting a proton), while sulfuric acid functions as an acid (by donating a proton). Therefore, the correct answer to the question is that the acids respectively function as a base and an acid.

### Final Answer:
- **Nitric acid acts as a base, and sulfuric acid acts as an acid.**