Question

why diffusion is not possible in solids

Answer 1

In simple terms Diffusion is defined as intermixing of particles due to their random motion.To diffuse or intermix there must be space in between the particles.It happens in gases in much faster rate than liquid but not at all in solid as in solid the particles can only vibrate on the spot, rather than being able to move from place to place and they are tightly packed so almost negligible space in between them.