Diffusion is said to be the movement of particles, molecules ions from a region where they are more concentrated to a region where they are less concentrated.
Diffusion does not require a semi - permeable membrane and is purely dependent upon the free energy of the diffusing substance only.
Ink particles spread (diffuse) from the drop of ink where they are more concentrated to all the part of the water in the beaker until they are evenly distributed, thus reaching a state of equilibrium.
