Diffusion can happen in solids as well. Solid-state diffusion is an extremely slow process. Solid particles have the lowest kinetic energy and so do not move. As a result, in the case of solids, diffusion takes a lengthy time.
Liquid diffusion is slower than gas diffusion. This is due to the fact that liquid particles travel more slowly than gas particles.
Gases have a very fast diffusion rate. Because gas particles move very swiftly in all directions. The rate of diffusion of a gas, on the other hand, is determined by its density.