Question

define following term(1) rigidity and (2)diffusion

Answer 1

rigidity means a body which is inflexible and unbending for example stone which is unbending and inflexible
diffusion means the movement of a molecule from a region of high concentration to the region of low concentration

Answer 2

Rigidity -

The property of solids being stiff and resist towards rest is called rigidity.

Diffusion-

Diffusion is a physical process that refers to the net movement of molecules from a region of high concentration to one of lower concentration.