Diffusion takes place in solid to …

Diffusion in gas:

Diffusion takes place most rapidly in gasses.

The particles of gas have more kinetic energy due to that they move with high speed. Because of the movement of particles with high speed gas diffuses most rapidly.

Example: Mixing of gases in air

Diffusion in liquid:

Diffusion takes place in liquids. The rate of diffusion is less in liquid than that of gases.

The particles of liquid have enough movement because of kinetic energy for diffusion. When two liquids are kept together they are mixed because of the diffusion.

For example; When salt solution is kept in water this makes whole the solution salty after some time. This happens because of diffusion in liquids.

Diffusion in solid:

Diffusion takes place with slowest rate in the case of solids. The rate of diffusion is almost negligible in solids.

Since the particles of solid have lowest kinetic energy so they do not move. Hence, diffusion takes a long time in the case of solid.

Example – Some time we observe that the marks of chalk on the black board could not be wiped out easily after a long time. This happens because of the diffusion of particles of chalks with the particles of black-board and marks of chalk could not be wiped out.