Introduction:
Liquefaction is the process of converting a gas into a liquid state. Liquefied gases have several practical applications, such as in industry, transportation, and refrigeration. However, not all gases can be easily liquefied. The process of liquefaction depends on the properties of the gas and the conditions under which it is subjected.

Explanation:
1. Increasing the temperature:
When we increase the temperature of a gas, its molecules gain kinetic energy and move faster. This causes the intermolecular forces between the molecules to weaken, and the gas expands. As a result, the gas becomes less likely to be liquefied. Therefore, increasing the temperature is not a suitable method for liquefying a gas.

2. Lowering the pressure:
Lowering the pressure is one of the key factors in liquefying a gas. According to the phase diagram of a substance, there is a critical temperature and pressure above which the substance cannot exist in a liquid state, regardless of the pressure applied. By lowering the pressure below this critical point, it becomes easier to liquefy the gas.

3. Increasing the pressure:
Increasing the pressure on a gas can also contribute to its liquefaction. When the pressure is increased, the gas molecules are brought closer together, and the intermolecular forces between them become stronger. As a result, the gas molecules are more likely to condense into a liquid state. However, increasing the pressure alone may not be sufficient to liquefy a gas, especially if the temperature is above the critical point.

4. Reducing the temperature:
Reducing the temperature of a gas decreases the kinetic energy of its molecules. As a result, the gas molecules move more slowly and have less energy to overcome the intermolecular forces. This increases the likelihood of the gas molecules coming close enough to form a liquid. Therefore, reducing the temperature is an effective method for liquefying a gas.

Conclusion:
In conclusion, the most effective method for liquefying a gas is by increasing the pressure and reducing the temperature simultaneously. Lowering the pressure allows the gas to exist in a liquid state by moving it away from its critical point, while reducing the temperature decreases the kinetic energy of the gas molecules, making them more likely to condense into a liquid.