Dear Student
Diffusion is the movement of particles from a region of higher concentration to a region of lower concentration.
Diffusion is the net movement of anything from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in concentration. so basically it is the process wherein the molecules merge as a result of their kinetic energy of random motion. It occurs in liquids and gases because their molecules move randomly. The molecules move from a region of higher concentration to a region of lower concentration, down the concentration gradient, until the concentration equalizes throughout the medium.
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