Brownian motion cause?

• A. The diffusion of solvent molecules
• B. The gravitational settling of particles
• C. The chaotic movement of colloidal particles due to collisions with solvent molecules
• D. The emission of light by colloids

Answer: (C)

Brownian motion comes from the random, continuous collisions between solvent molecules and the suspended particles. Each collision transfers a small amount of momentum, and because the collisions occur unpredictably in time and direction, the particle takes on a jagged, chaotic path. This motion is a direct result of the thermal energy driving solvent molecules, not from the solvent molecules simply diffusing on their own or from gravity pulling the particles, and it isn’t caused by light emission. In short, the erratic jitter of the particle reflects momentum transfer from constantly moving solvent molecules.