Which of the following gas cannot be collected over water dutring its preparation

Options

A. oxygen
B. Nitrogen
C. Hydrogen
D. Hydrogen chloride

Answer

To determine which gas cannot be collected over water during its preparation, we need to analyze the behavior of each gas with water. Here’s a step-by-step solution:

### Step 1: Understand the Concept
Gases can be collected over water if they do not react with water. If a gas reacts with water, it will form new substances, making it impossible to collect the original gas.

### Step 2: Analyze Each Option
1. **Oxygen (O2)**:
- Reaction: O2 + H2O → No reaction.
- Conclusion: Oxygen does not react with water, so it can be collected over water.

2. **Nitrogen (N2)**:
- Reaction: N2 + H2O → No reaction.
- Conclusion: Nitrogen does not react with water, so it can be collected over water.

3. **Hydrogen (H2)**:
- Reaction: H2 + H2O → No reaction.
- Conclusion: Hydrogen does not react with water, so it can be collected over water.

4. **Hydrogen Chloride (HCl)**:
- Reaction: HCl + H2O → H3O+ + Cl- (reacts with water).
- Conclusion: HCl reacts with water to form hydronium ions and chloride ions, so it cannot be collected over water.

### Step 3: Final Conclusion
Based on the analysis, the gas that cannot be collected over water during its preparation is **Hydrogen Chloride (HCl)**.

### Answer:
**Hydrogen Chloride (HCl)** cannot be collected over water.

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