Final answer:
The temperature on the Kelvin scale where all molecular activity stops is 0 K, also known as absolute zero.
Step-by-step explanation:
The temperature on the Kelvin scale where all molecular activity stops is 0 K, also known as absolute zero. It is the point at which all molecular motion ceases. The Kelvin scale is based on molecular motion, with 0 K representing absolute zero, while the freezing point of water on the Kelvin scale is 273.15 K and the boiling point is 373.15 K.