The gas which will be most easily liquefied is

Options

A. He
B. `O_2`
C. `NH_3`
D. `CO_2`

Answer

To determine which gas is most easily liquefied among the given options (helium, oxygen, ammonia, and carbon dioxide), we can analyze their properties and intermolecular forces.

### Step-by-Step Solution:

1. **Understanding Liquefaction**:
- Liquefaction of gases occurs when the gas molecules are brought close enough together to form a liquid. This typically requires a reduction in temperature or an increase in pressure.

2. **Intermolecular Forces**:
- The strength of intermolecular forces plays a crucial role in the liquefaction of gases. Stronger intermolecular forces lead to easier liquefaction.
- The main types of intermolecular forces are:
- Van der Waals forces (dispersion forces)
- Dipole-dipole interactions
- Hydrogen bonding

3. **Analyzing the Given Gases**:
- **Helium (He)**: A noble gas with very weak van der Waals forces due to its monoatomic nature. It is not easily liquefied.
- **Oxygen (O2)**: A diatomic molecule with weak van der Waals forces. It can be liquefied, but not as easily as some other gases.
- **Ammonia (NH3)**: This molecule can form hydrogen bonds due to the presence of nitrogen, which is highly electronegative. Hydrogen bonding is a strong intermolecular force, making ammonia more easily liquefiable.
- **Carbon Dioxide (CO2)**: This gas has dipole-dipole interactions and some van der Waals forces, but it does not form hydrogen bonds, making it less easily liquefiable than ammonia.

4. **Conclusion**:
- Among the gases listed, ammonia (NH3) has the strongest intermolecular forces due to hydrogen bonding. Therefore, it is the gas that can be most easily liquefied.

5. **Final Answer**:
- The gas which will be most easily liquefied is **Ammonia (NH3)**.