The coldest temperature, 0 Kelvin, that can be reached. It is the hypothetical temperature at which all molecular motion stops.

The coldest temperature, 0 Kelvin, that can be reached. It is the hypothetical temperature at which all molecular motion stops.

• A. Freezing
• B. Absolute zero
• C. Melting point
• D. Boiling point

Answer: (B)

Absolute zero is the lowest possible temperature, defined as 0 kelvin on the Kelvin scale, where in theory all molecular motion would stop. In practice, quantum mechanics ensures there is always some zero-point motion, so we can approach absolute zero very closely but never reach it exactly. The other terms describe specific phase changes: freezing is the process of a liquid becoming a solid at a given temperature and pressure; melting point is the temperature at which a solid becomes a liquid; boiling point is the temperature at which a liquid becomes a gas. These are not universal limits but particular transition temperatures for substances under certain conditions.

Absolute zero is the lowest possible temperature, defined as 0 kelvin on the Kelvin scale, where in theory all molecular motion would stop. In practice, quantum mechanics ensures there is always some zero-point motion, so we can approach absolute zero very closely but never reach it exactly. The other terms describe specific phase changes: freezing is the process of a liquid becoming a solid at a given temperature and pressure; melting point is the temperature at which a solid becomes a liquid; boiling point is the temperature at which a liquid becomes a gas. These are not universal limits but particular transition temperatures for substances under certain conditions.