Question

why solids don't diffuse one another. ​

Answer 1

Solid particles have relatively low energies compared to liquid and gas particles, so they are less likely to move appreciably within the bulk that surrounds them. Solid particles are much closer together than the particles in a gas, so there is less space for a particle to invade between other particles.

Answer 2

Solid particles have relatively low energies compared to liquid and gas particles, so they are less likely to move appreciably within the bulk that surrounds them. Solid particles are much closer together than the particles in a gas, so there is less space for a particle to invade between other particle.

so they diffuse easily....