Which one of the following gases has the highest critical temperature ?

Options

A. Nitrogen
B. Ammonia
C. Water vapours
D. Carbon dioxide

Explanation

To determine which gas has the highest critical temperature among the given options (nitrogen, ammonia, water vapor, and carbon dioxide), we can follow these steps:

### Step-by-Step Solution:

1. **Understand Critical Temperature**:
- The critical temperature of a substance is the temperature above which it cannot be liquefied, regardless of the pressure applied.

2. **Identify Factors Affecting Critical Temperature**:
- The critical temperature is influenced by intermolecular forces, particularly hydrogen bonding. The stronger the intermolecular forces, the higher the critical temperature.

3. **Analyze the Given Gases**:
- **Nitrogen (N2)**: This is a nonpolar molecule with weak van der Waals forces. It has a low critical temperature.
- **Ammonia (NH3)**: Ammonia exhibits hydrogen bonding, which is stronger than van der Waals forces. Its critical temperature is higher than that of nitrogen.
- **Water Vapor (H2O)**: Water has strong hydrogen bonding due to its molecular structure, allowing it to form multiple hydrogen bonds. It has a very high critical temperature.
- **Carbon Dioxide (CO2)**: Carbon dioxide has a higher critical temperature than nitrogen but lower than ammonia and water due to its molecular structure and the type of intermolecular forces present.

4. **Compare Critical Temperatures**:
- To find the gas with the highest critical temperature, we need to compare the known critical temperatures:
- Nitrogen: -196 °C
- Ammonia: -33 °C
- Water: 374 °C
- Carbon Dioxide: 31 °C

5. **Conclusion**:
- Among the gases listed, water vapor has the highest critical temperature at 374 °C. Therefore, the answer is **water vapor**.

### Final Answer:
Water vapor has the highest critical temperature among the given options.

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