Step 1:

(i) Lyophilic sols:

Colloidal sols that are formed by mixing substances such as gum, gelatin, starch, etc. with a suitable liquid (dispersion medium) are called lyophilic sols.

These sols are reversible in nature i.e., if two constituents of the sol are separated by any means (such as evaporation), then the sol can be prepared again by simply mixing the dispersion medium with the dispersion phase and shaking the mixture.

For examples: Gum sol, starch sol, rubber, gelatin, egg albumin sol , etc. 

(ii) Lyophobic sols:

When substances such as metals and their sulfides etc. are mixed with the dispersion medium, they do not form colloidal sols. Their colloidal sols can be prepared only by special methods. Such sols are called lyophobic sols.

These sols are irreversible in nature. Lyophobic sols need stabilizing agents for their preservation. 

Examples of Lyophobic Sols – Ferric hydroxide sol, aluminum hydroxide sol, arsenious sulfide sol, etc.

Step 2:

Hydrophobic sols get easily coagulated because these sols are stabilized due to the charge on the particle. If the charge is removed by adding any suitable electrolyte the particles tend to come closer and form aggregate or precipitate.