Gas that can not be collected over water is:

Options

A. `N_(2)`
B. `O_(2)`
C. `SO_(2)`
D. `PH_(3)`

Explanation

To solve the question "Gas that cannot be collected over water is:", we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: We need to identify a gas that cannot be collected over water. This typically refers to gases that react with water.

2. **Identify Gases**: Consider common gases that are known to react with water. Some examples include sulfur dioxide (SO2), hydrogen chloride (HCl), and ammonia (NH3).

3. **Analyze the Reactions**:
- **Sulfur Dioxide (SO2)**: When SO2 comes into contact with water, it reacts to form sulfurous acid (H2SO3):
\[ \text{SO}_2 (g) + \text{H}_2\text{O} (l) \rightarrow \text{H}_2\text{SO}_3 (aq) \]
- **Hydrogen Chloride (HCl)**: HCl also reacts with water to form hydrochloric acid:
\[ \text{HCl} (g) + \text{H}_2\text{O} (l) \rightarrow \text{H}_3\text{O}^+ (aq) + \text{Cl}^- (aq) \]
- **Ammonia (NH3)**: Ammonia reacts with water to form ammonium hydroxide:
\[ \text{NH}_3 (g) + \text{H}_2\text{O} (l) \rightarrow \text{NH}_4\text{OH} (aq) \]

4. **Determine the Correct Answer**: Among the gases mentioned, sulfur dioxide (SO2) is a common example that cannot be collected over water because it reacts with water to form a solution, thus making it impossible to collect as a gas.

5. **Conclusion**: Therefore, the gas that cannot be collected over water is **sulfur dioxide (SO2)**.

### Final Answer:
The gas that cannot be collected over water is **SO2 (sulfur dioxide)**.

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