(i) In multi-molecular colloids in which the colloidal particles are consist of small molecules with a diameter of less than 1 nm. The molecules are formed aggregate and held together by van der Waal s forces. Examples of such colloids include gold sol and sulphur sol.

(ii) In macro-molecular colloids in which the colloidal particles are large molecules having colloidal dimensions. These particles have a high molecular mass. When these particles are dissolved in a liquid, sol is obtained. For example: starch, nylon, cellulose, etc.

(iii) Certain substances tend to behave like normal electrolytes at lower concentrations. However, at higher concentrations, these substances behave as colloidal solutions due to the formation of aggregated particles. Such colloids are called aggregated colloids.