Explain the following giving suitable reasons: In the manufacture of `H_2SO_4` by contact process:
The impurity of arsenic oxide must be removed before passing the mixture of `SO_2` and air through the catalytic chamber. 

Explanation

### Step-by-Step Solution:

1. **Understanding the Contact Process**: The contact process is the industrial method used to produce sulfuric acid (H₂SO₄). It involves the oxidation of sulfur dioxide (SO₂) to sulfur trioxide (SO₃) using a catalyst, typically vanadium pentoxide (V₂O₅), in the presence of oxygen (from air).

2. **Role of the Catalyst**: In the contact process, the catalyst is crucial because it increases the rate of the reaction without being consumed. The reaction can be represented as:
\[ 2SO₂(g) + O₂(g) \xrightarrow{V₂O₅} 2SO₃(g) \]
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