Which statement about gases is true?
they are made up of particles that always move very slowly.
they are made up of particles that travel in a curved path when in motion.
they are made up of hard spheres that vibrate quickly in stationary positions.
they are made up of hard spheres that are in random motion.

Option (d) is the correct answer.

Explanation:

A gas is a state of matter in which particles are away from each other because they are held by weak Vander waal forces. This leads to gain in kinetic energy of the particles and they move rapidly from one place to another.

As a result, particles of a gas moves randomly.

Therefore, we can conclude that the statement they are made up of hard spheres that are in random motion, is true about gases.