The critical temperature of a substance is the highest temperature at which the substance may be in a ____ state, regardless of the pressure applied to it.

The critical temperature of a substance is indeed the highest temperature at which it can maintain a liquid state, regardless of the pressure applied. Above this temperature, no matter how much pressure is applied, the substance cannot exist as a liquid; it will remain in a gaseous state. This concept is fundamental in understanding phase diagrams and the behavior of materials under various temperature and pressure conditions.

The designation of the highest temperature for the liquid state is crucial in various applications, particularly in refrigeration and air conditioning, where the performance of refrigerants depends significantly on their thermal properties and phase transitions. Recognizing the critical temperature helps in selecting appropriate working fluids that will operate efficiently within specific temperature ranges.