Biology

The correct answer is: C.Down the concentration gradient.

Explanation:

During diffusion, molecules move from an area of higher concentration to an area of lower concentration. This process occurs naturally due to the random movement of molecules and continues until the concentrations of the molecules are evenly distributed, achieving equilibrium.

A.Up the concentration gradient: This is not how diffusion works. Molecules move down the concentration gradient (from high to low concentration) in diffusion. Moving up the gradient would require energy (i.e., active transport).