What is the primary factor that affects the temperature of a substance?

The primary factor that affects the temperature of a substance is the average kinetic energy of its particles. Temperature is defined as a measure of the average energy of random motion of the particles in a substance. As the kinetic energy increases, the temperature rises, indicating that the particles are moving faster and are more energetic. This relationship is fundamental in thermodynamics, as it helps explain how heat transfer can raise or lower the temperature of a material.

The other factors listed can influence temperature, but they do not serve as direct measurements of it. For instance, while mass can play a role in the total thermal energy of a substance, it does not determine temperature on its own. Similarly, the amount of heat energy present relates to the total energy within a system rather than the temperature directly. The type of substance can affect how it responds to heat and how heat is distributed among its particles, but it is the kinetic energy that is a defining characteristic of temperature itself.