Which phenomenon describes light scattering in colloids?

• A. Brownian motion
• B. Refraction
• C. Diffusion
• D. Tyndall effect

Answer: (D)

The main concept is light scattering by colloidal particles, known as the Tyndall effect. In a colloid, the dispersed particles are just large enough to scatter visible light as it passes through the medium. This scattering makes the beam of light visible inside the colloid, so you can often see a distinct shaft of light in mixtures like milk or fog. In a true solution, particles are too small to scatter light, so the beam isn’t visible. Refraction is simply the bending of light at interfaces, and diffusion describes the spreading of particles due to random motion, not how light interacts with the mixture. Brownian motion explains the microscopic jitter of particles, not light scattering. So the described phenomenon is the Tyndall effect.