Consider the diagram. Top: A ball is shown traveling left to right toward an identical stationary ball. Middle: the first ball hits the second ball. Bottom: The right-hand ball travels to the right away from the left-hand ball, which is now stationary. Which postulate of the kinetic-molecular theory best describes the event in the diagram?

Most of the volume of a gas is empty space.
All collisions between particles are perfectly elastic.
There is no force of attraction or repulsion between gas particles.
The average kinetic energy of particles depends only on temperature.