In the laboratory preparation of carbon dioxide, carbon dioxide is collected by:

Options

A. downward displacement of water
B. upward displacement of water
C. downward displacement of air
D. upward displacement of air

Answer

To solve the question about how carbon dioxide is collected in the laboratory preparation, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Preparation of Carbon Dioxide**:
- Carbon dioxide (CO2) is commonly prepared in the laboratory by the reaction of calcium carbonate (CaCO3) with hydrochloric acid (HCl).
- The chemical reaction is:
\[ \text{CaCO}_3 + 2 \text{HCl} \rightarrow \text{CaCl}_2 + \text{H}_2\text{O} + \text{CO}_2 \]
- This reaction produces calcium chloride, water, and carbon dioxide gas.

2. **Identify the Properties of Carbon Dioxide**:
- Carbon dioxide is denser than air but less dense than water.
- This means that when CO2 is produced, it will behave differently compared to lighter gases.

3. **Determine the Collection Method**:
- Since carbon dioxide is denser than air, it will accumulate at the bottom of a container.
- Therefore, the appropriate method for collecting carbon dioxide is by **upward displacement of air**. This means that as CO2 is produced, it pushes the lighter air upwards, allowing CO2 to fill the container from the bottom.

4. **Select the Correct Option**:
- Given the options:
1. Downward displacement of water
2. Upward displacement of water
3. Downward displacement of air
4. Upward displacement of air
- The correct answer is option **4: Upward displacement of air**.

### Final Answer:
Carbon dioxide is collected by **upward displacement of air**.

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