Due to the constant random motion of its atoms and molecules, a substance will exhibit net movement from a region where it has a higher concentration to a region where it has a lower concentration.
this net movement is called

The net movement is called diffusion.

Explanation:

Diffusion is the net movement of substance from region of higher concentration to a region of lower concentration.

The movement is due to constant and random motion characteristics of atoms ,ions and molecules due to kinetic energy. It continues until the concentration of substance is uniform.

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