What is the maximum temperature at which a gas can be converted into a liquid called?

The maximum temperature at which a gas can be converted into a liquid is known as the critical temperature. At this temperature, the kinetic energy of the gas molecules is such that they cannot be condensed into a liquid by applying pressure alone. Above this temperature, no amount of pressure can turn the gas into a liquid, which is significant because it defines the limits of the phase transition from gas to liquid.

Understanding critical temperature is essential in various scientific and industrial applications, including the behavior of gases in different temperature ranges and the design of equipment involving gas liquefaction. The concept is pivotal in thermodynamics and physical chemistry, particularly when studying the properties of substances and their transitions between states.

Other terms like "optimal temperature," "boiling temperature," and "freezing temperature" refer to different thermodynamic processes and phenomena and do not accurately describe the conditions for liquefying a gas under critical conditions. Boiling temperature is related to phase changes from liquid to gas, while freezing temperature pertains to solidification processes. Hence, critical temperature specifically denotes the point of no return for gas to liquid transitions and is the correct term for this question.