Final answer:
All molecular motion theoretically ceases at absolute zero, which is 0 K on the Kelvin temperature scale, where particles have no kinetic energy.
Step-by-step explanation:
Theoretically, all molecular motion would stop at 0 K, which is known as absolute zero. At absolute zero, the temperature at which all molecular motion theoretically ceases, particles have no kinetic energy. Molecular motion includes vibrational, rotational, and translational movements, all of which would be absent at this temperature. While absolute zero has never been achieved in the laboratory, temperatures very close to it have been attained. The Kelvin temperature scale is directly proportional to the average kinetic energy of particles, making it the relevant scale for examining phenomena at extremely low temperatures like absolute zero.