The common impurity in sulphur dioxide used in contact process 

Options

A. `SO_(3)`
B. `CO_(2)`
C. `As`
D. `As_(2)O_(3)`

Answer

To solve the question regarding the common impurity in sulfur dioxide used in the contact process, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Contact Process**:
The contact process is a method used to produce sulfuric acid (H₂SO₄) from sulfur dioxide (SO₂). The overall reaction involves the oxidation of sulfur dioxide to sulfur trioxide (SO₃) using oxygen (O₂) in the presence of a catalyst.

2. **Identify the Catalyst Used**:
In the contact process, platinum (Pt) is often used as a catalyst for the reaction between sulfur dioxide and oxygen to form sulfur trioxide.

3. **Consider Impurities in Sulfur Dioxide**:
The question asks for the common impurity found in sulfur dioxide that can affect the catalytic process. Impurities can interfere with the catalyst's effectiveness.

4. **Evaluate the Given Options**:
The options provided are:
- SO₃
- CO₂
- As (Arsenic)
- As₂O₃ (Arsenic Trioxide)

5. **Identify the Common Impurity**:
Among the options, As₂O₃ (Arsenic Trioxide) is known to be a common impurity in sulfur dioxide. It acts as a poison for the platinum catalyst, reducing its catalytic activity.

6. **Conclusion**:
Therefore, the common impurity in sulfur dioxide used in the contact process is As₂O₃.

### Final Answer:
The common impurity in sulfur dioxide used in the contact process is **As₂O₃** (Arsenic Trioxide).

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