Suspends light like fog.

Suspends light like fog.

• A. Colloid
• B. Solution
• C. Pure substance
• D. Heterogeneous mixture

Answer: (A)

Suspending light through a medium is a hallmark of a colloid, due to the Tyndall effect where particles scatter visible light. Fog is a colloidal dispersion: tiny droplets of liquid water scattered throughout air. These droplets are large enough to scatter light so you can see a beam through fog, yet small enough to stay suspended rather than settle out. A true solution has solute particles that are too small to scatter light and form a fully uniform mixture, so you don’t see the beam. A pure substance is a single component, not a mixture. A heterogeneous mixture can contain different parts, but the key feature described here—the light-scattering behavior that makes the beam visible—is specifically characteristic of colloids.

Suspending light through a medium is a hallmark of a colloid, due to the Tyndall effect where particles scatter visible light. Fog is a colloidal dispersion: tiny droplets of liquid water scattered throughout air. These droplets are large enough to scatter light so you can see a beam through fog, yet small enough to stay suspended rather than settle out.

A true solution has solute particles that are too small to scatter light and form a fully uniform mixture, so you don’t see the beam. A pure substance is a single component, not a mixture. A heterogeneous mixture can contain different parts, but the key feature described here—the light-scattering behavior that makes the beam visible—is specifically characteristic of colloids.