In diffusion, molecules move from an area of high concentration to an area of low concentration until equilibrium is reached. Which option correctly represents this concept?

• A. Equilibrium
• B. Maximum concentration
• C. Destination
• D. Saturation

Answer: (A)

Diffusion moves molecules down their concentration gradient—from areas of high concentration to areas of low concentration—until the concentrations on both sides become equal. This resulting state is equilibrium, where there is no net movement of molecules because the two directions balance out, even though individual molecules keep moving randomly. That balance is what diffusion aims for: a uniform distribution. Terms like maximum concentration, destination, or saturation don’t describe this process: maximum concentration isn’t about reaching a balance across space, destination is vague, and saturation relates to how much solute a solvent can hold rather than how particles spread out.