Which of the following best defines diffusion?

Diffusion is best defined as the net movement of particles from areas of high concentration to areas of low concentration. This process occurs naturally and does not require energy. It is driven by the concentration gradient, which is the difference in concentration between two areas. Over time, particles will spread out evenly until equilibrium is reached, meaning there is no longer a concentration gradient. This process is crucial for many biological functions, such as the exchange of gases in the lungs and the movement of nutrients and waste products in and out of cells.