In the preparation of `H_2SO_4` the catalyst and the inhibitor, respectively, are

Options

A. platinum, molybdenum
B. iron, arsenic oxide
C. platinum, arsenic oxide
D. iron, molybdenum

Explanation

To answer the question regarding the preparation of sulfuric acid (H₂SO₄), we need to identify the catalyst and the inhibitor used in the process.

### Step-by-Step Solution:

1. **Understanding the Reaction**:
- The preparation of sulfuric acid involves the contact process, which begins with the oxidation of sulfur dioxide (SO₂) to sulfur trioxide (SO₃).
- The overall reaction can be summarized as:
\[ \text{S} + \text{O}_2 \rightarrow \text{SO}_2 \]
\[ \text{2SO}_2 + \text{O}_2 \rightarrow \text{2SO}_3 \]

2. **Catalyst Identification**:
- In the contact process, a catalyst is used to speed up the reaction without being consumed. The catalyst for the conversion of SO₂ to SO₃ is **platinum (Pt)**. Platinum is known for its effectiveness in catalyzing this reaction.

3. **Inhibitor Identification**:
- An inhibitor is a substance that slows down or prevents a chemical reaction. In the case of the contact process for sulfuric acid production, **arsenic oxide (As₂O₃)** is used as an inhibitor. It helps to control the reaction rate and prevent the formation of unwanted by-products.

4. **Conclusion**:
- Therefore, the catalyst and the inhibitor used in the preparation of sulfuric acid (H₂SO₄) are:
- **Catalyst**: Platinum (Pt)
- **Inhibitor**: Arsenic oxide (As₂O₃)

### Final Answer:
- The catalyst and the inhibitor, respectively, in the preparation of H₂SO₄ are **platinum (Pt)** and **arsenic oxide (As₂O₃)**.