Which theory of matter states that all particles of matter are in constant motion?

The correct answer is KINETIC THEORY. Kinetic theory states that matters are made up of small particles which are constantly in motion. The kinetic theory helps to explain the behavior of the particles of solids, liquid and gases. For instance, the theory explain that the particle of gases are far apart because of the weak intermolecular forces among them and they are always in constant, random motion, colliding with one another and with the wall of the container.