Oxygen is denser than air so it is collected over

Options

A. `H_(2)O`
B. Ethanol
C. Mercury
D. Kerosene oil

Answer

To answer the question "Oxygen is denser than air, so it is collected over...", we need to analyze the properties of oxygen and the methods of gas collection.

### Step-by-Step Solution:

1. **Understanding the Density of Oxygen**:
- Oxygen (O2) has a density of about 1.43 g/L at standard temperature and pressure (STP), which is denser than air (approximately 1.29 g/L). This means that oxygen will sink in air.

**Hint**: Remember that gases can be collected based on their density relative to air.

2. **Collection Methods for Gases**:
- Gases can be collected using different methods such as over water, over mercury, or through displacement of air. The method chosen often depends on the solubility of the gas in the collecting medium.

**Hint**: Consider the solubility of the gas in the medium when choosing a collection method.

3. **Solubility of Oxygen**:
- Oxygen is only slightly soluble in water (about 0.003 g per 100 mL at room temperature). This means that when collecting oxygen, using water would not be effective, as it would dissolve in it.

**Hint**: Think about how solubility affects the collection of gases.

4. **Choosing the Right Medium**:
- Since oxygen is denser than air and not very soluble in water, it can be collected over water. However, if we consider other options like mercury or kerosene, we find that oxygen is not soluble in mercury and kerosene either.

**Hint**: Compare the solubility of oxygen in different liquids to determine the best collection method.

5. **Conclusion**:
- The best method for collecting oxygen, given that it is denser than air and not soluble in water, mercury, or kerosene, is to use a gas jar inverted over a trough of water. However, since the question specifically asks for a method, the answer is that oxygen is collected over water due to its low solubility.

**Final Answer**: Oxygen is collected over water.