What type of property is internal energy?

Internal energy is classified as an extensive property because it depends on the amount of substance present in the system. As the quantity of material increases, the internal energy also increases, reflecting the total energy contained within the material.

Additionally, internal energy is a state function, meaning that its value is determined only by the state of the system, which can be defined by variables such as temperature, pressure, and volume. It does not depend on the path taken to reach that state; rather, it is a characteristic of the specific conditions in which the substance exists.

Thus, the combination of being extensive and a state function is what correctly defines internal energy.