Which of the following gas is not dried by conc. `H_(2)SO_(4)` ?

Options

A. HCl
B. HBr
C. `H_(2)S`
D. `SO_(2)`

Explanation

To determine which gas is not dried by concentrated sulfuric acid (H₂SO₄), we need to analyze the properties of the gases provided and how they interact with concentrated H₂SO₄.

### Step-by-Step Solution:

1. **Understand the Properties of Concentrated H₂SO₄**:
- Concentrated sulfuric acid is a strong dehydrating agent and is used to dry gases. However, it can also react with certain gases, especially those that are acidic or can be oxidized.

2. **Identify the Gases**:
- The gases mentioned in the question are HCl (hydrochloric acid), H₂S (hydrogen sulfide), HBr (hydrobromic acid), HI (hydroiodic acid), and SO₂ (sulfur dioxide).

3. **Analyze Each Gas**:
- **HCl**: Hydrochloric acid is a strong acid but does not react with concentrated H₂SO₄. It can be dried by H₂SO₄.
- **H₂S**: Hydrogen sulfide is a weak acid and can be oxidized by concentrated H₂SO₄, thus it cannot be dried by it.
- **HBr**: Hydrobromic acid can also be oxidized by concentrated H₂SO₄, so it cannot be dried by it.
- **HI**: Hydroiodic acid can similarly be oxidized by concentrated H₂SO₄, making it unable to be dried.
- **SO₂**: Sulfur dioxide is a strong acid and does not react with concentrated H₂SO₄, so it can be dried.

4. **Conclusion**:
- The gases that cannot be dried by concentrated H₂SO₄ are H₂S, HBr, and HI due to their ability to be oxidized. However, HCl and SO₂ do not react with H₂SO₄, indicating they can be dried.

### Final Answer:
The gas that is not dried by concentrated H₂SO₄ is **H₂S** (hydrogen sulfide).