Final answer:
The true statement about kinetic molecular theory is that temperature affects the average kinetic energy of gas particles. Gas particles are constantly moving, with collisions being elastic and intermolecular forces being negligible. As temperature increases, the kinetic energy of the particles also increases.
Step-by-step explanation:
The statement about kinetic molecular theory that is true is: C) Temperature affects the average kinetic energy of gas particles. According to the theory, gas particles are in a state of constant and random motion, and collisions between particles and with the container are elastic, meaning there is no net loss of kinetic energy. Moreover, kinetic molecular theory asserts that there are negligible intermolecular forces in a gas, and that the average kinetic energy of gas particles is proportional to the temperature of the gas, as measured in Kelvin. This means that as temperature increases, the particles move faster and have greater kinetic energy. Statements A and B are incorrect because gas particles are always in motion, and increasing pressure at constant temperature generally decreases the volume of a gas, according to Boyle's Law. Statement D is incorrect because in a solid, the particles are not free to move past each other; they are locked in place and can only vibrate.