Q.By which property of a colloid can we distinguish between a colloidal solution and a true solution of the same colour?

Three properties provide direct experimental evidence for colloidal particles' size, motion and charge. The

Tyndall effect is the scattering of a light beam by colloidal particles, making its path visible from the

side as an illuminated cone — it occurs because colloidal particles are large enough (comparable to or larger

than the wavelength of visible light) to scatter light effectively, unlike the far smaller particles of a true

solution, which scatter negligibly; dust visible in a slanting sunbeam and a car's headlight beam in fog are

everyday examples.

Brownian movement is the continuous, random, zig-zag motion of colloidal particles, caused by the constant,

directionally unequal bombardment of each particle by the far smaller, faster-moving molecules of the dispersion

medium. This ceaseless agitation opposes gravitational settling and is a key source of a colloid's kinetic

stability — its ability to stay dispersed indefinitely despite not being thermodynamically stable. …