What thermal concept is reached at 0 K in the Kelvin scale?

The concept reached at 0 K on the Kelvin scale is known as Absolute Zero. Absolute Zero is defined as the theoretical temperature at which all molecular motion ceases. It represents the lowest possible temperature, where a system reaches its minimum internal energy. At this point, it is believed that a substance is in its most ordered state, and no heat energy remains to be extracted from it.

To provide additional context, the freezing point generally refers to the temperature at which a substance changes from a liquid to a solid, which occurs at different temperatures depending on the substance and atmospheric pressure. The melting point similarly refers to the transition from solid to liquid. The critical point, on the other hand, indicates the highest temperature and pressure at which a phase of a substance can exist, beyond which distinct liquid and gas phases do not exist. In contrast, Absolute Zero is a fundamental thermodynamic limit in physics and is crucial for understanding temperature scales and the behavior of matter at extremely low temperatures.