Final answer:
Temperature is best described as the motion of molecules (option 2), specifically it is related to the average kinetic energy of the particles within a substance. It is not related to the number, size, or type of molecules, but rather to their energy of motion with absolute zero representing a lack of molecular motion.
Step-by-step explanation:
The best description of temperature among the given options is motion of molecules. Temperature is related to the average kinetic energy of atoms and molecules within a substance. It's a measure of the average energy of motion, otherwise known as thermal energy, that particles have. When we talk about absolute zero, we refer to the point at which molecules would have no motion at all. In practical terms, as the temperature of a substance increases, so does the motion of its molecules.
Regarding kinetic theory, this energy and motion relate to how gas particles, when contained, exert pressure on their container as they collide against its walls. These particles move in random directions with varying speeds, but the overall motion can be related to the substance's temperature. Further, the kinetic theory also tells us that if two gases have the same temperature but different molecular masses, they will exert the same pressure even though their molecules may have different speeds.
Therefore, the concept of temperature is fundamentally associated with the random motion of molecules and atoms within a material, not their quantity, size, or type. Understanding this helps us grasp the behavior of substances under different thermal conditions.