Q.Choose the correct option.
Gum in water is an example of
a. true solution
b. suspension
c. lyophilic sol
d. lyophobic sol

Colloids are classified in three independent ways. By physical state of dispersed phase and dispersion medium: eight combinations are possible, giving solid sols (e.g. coloured glass), sols/gels (e.g. paints, muddy water), aerosols (solid- or liquid-in-gas, e.g. smoke or fog), emulsions (liquid-in-liquid, e.g. milk), and foams (gas-in-liquid or gas-in-solid, e.g. whipped cream, foam rubber). By affinity between the phases: lyophilic colloids (particles with strong affinity for the medium, e.g. starch, gum) are reversible, self-stabilised and hard to coagulate; lyophobic colloids (little/no affinity, e.g. Ag, Au sols, metal-hydroxide sols) are irreversible, unstable without added stabilisers, and coagulate easily. By molecular size: multimolecular colloids are aggregates of many small atoms/molecules held by van der Waals forces (e.g. a gold sol, S8 sulfur); macromolecular colloids are single molecules already large enough to be colloidal (e.g. starch, proteins, nylon); and associated colloids (micelles) are substances like soap or detergent that behave as normal electrolytes at low concentration but, above a critical concentration, associate into spherical micelles -- hydrophobic hydrocarbon tails pointing inward, hydrophilic (carboxylate) heads facing outward into the water -- which is what makes a soap dispersion stable and gives soap its cleansing action.