Which of the following are the most favourable conditions for liefying a gas?

The liquefaction of a gas is the process of converting a gaseous substance into a liquid state. This transition is most effectively achieved under conditions of high pressure and low temperature. Increasing the pressure compresses the gas molecules, forcing them closer together and increasing their density. Simultaneously, lowering the temperature reduces the kinetic energy of the gas particles, which allows intermolecular attractive forces to become strong enough to hold the particles in a liquid phase. Every gas has a specific 'critical temperature' above which it cannot be liquefied, regardless of the amount of pressure applied. Therefore, to successfully liquefy a gas, it must be cooled below its critical temperature and subjected to sufficient pressure to overcome the remaining kinetic motion of the particles.

Sources

1. [1] Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 9: The Amazing World of Solutes, Solvents, and Solutions > 9.5.3 Effect of pressure on density > p. 148