Concept:A colloid is stable because its dispersed particles remain suspended in the dispersion medium indefinitely.
Explanation:Colloidal particles are very small, ranging from
10−9 m to
10−6 m in size.
When left undisturbed, these particles do not settle down under gravity.
This happens because of Brownian motion, the continuous random zigzag movement of particles caused by collisions with molecules of the dispersion medium.
Brownian motion opposes the downward pull of gravity, keeping the particles suspended.
Additionally, all particles of a colloid carry similar electrical charges.
These like charges repel one another, preventing the particles from clumping into heavier aggregates that would settle.
In contrast, suspensions settle because their particles are larger, whereas true solutions remain stable due to complete molecular dissolution.
Colloidal particles cannot be separated by ordinary filtration, but can be separated using centrifugation or ultrafiltration.
Answer:C. Its particles do not settle down when left undisturbed.