What is necessary for diffusion to occur?

• A. Pressure gradient
• B. Energy input
• C. Concentration gradient
• D. Time

Answer: (C)

For diffusion to take place, the presence of a concentration gradient is essential. This gradient refers to the difference in the concentration of a substance across a space. Molecules naturally move from areas of higher concentration to areas of lower concentration in order to reach equilibrium. This process is driven by the inherent kinetic energy of the molecules themselves and does not require any external energy input.

While pressure can influence the movement of molecules in certain scenarios, and time is a necessary factor for diffusion to occur over a distance, these elements are not prerequisites for diffusion itself. The fundamental requirement for diffusion is the concentration gradient, which provides the driving force for the movement of molecules and leads to the process of spreading out to achieve uniform concentration throughout a given space.