What measurement indicates the average kinetic energy of particles in a substance?

The measurement that indicates the average kinetic energy of particles in a substance is temperature. Temperature quantifies how fast the particles within a substance are moving — the higher the temperature, the greater the average kinetic energy of the particles. This relationship explains why substances tend to expand when heated; as particles gain kinetic energy, they move more vigorously, increasing the space between them.

In contrast, pressure is the force exerted by the particles of a substance as they collide with the walls of their container or with each other, but it does not directly measure their kinetic energy. Volume pertains to the amount of space that a substance occupies, and density is the mass of an object divided by its volume, which does not provide information about the energy of the particles. Temperature is thus the key measurement that connects to the motion and energy of particles in any given substance.