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(i) Inmulti-molecular colloids, the colloidal particles are an aggregate of atoms orsmall molecules with a diameter of less than 1 nm. The molecules in theaggregate are held together by van der Waal’s forces of attraction. Examples ofsuch colloids include gold sol and sulphur sol.
(ii) Inmacro-molecular colloids, the colloidal particles are large molecules havingcolloidal dimensions. These particles have a high molecular mass. When theseparticles are dissolved in a liquid, sol is obtained. For example: starch,nylon, cellulose, etc.
(iii) Certainsubstances tend to behave like normal electrolytes at lower concentrations.However, at higher concentrations, these substances behave as colloidalsolutions due to the formation of aggregated particles. Such colloids arecalled aggregated colloids.