Dear student,
The particles are the constituent units of matter and they move continuously inside the matter. All the particles of matter possess kinetic energy which causes these particles to be in continuous motion.
Mixing of gases in nature is also the evidence of motion of particles. We get the scent of our favourite food sitting in the drawing room while food is being cooked in the kitchen. This happens because vapour coming out from the hot food mixes with air comes to your nostril because of the motion of their particles.
This proves that particles of matter are in motion continuously.
Regards