Why hydrophobic sols are easily coagulated ?

(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.
(ii) Lyophobic sols:
When substances such as metals and their sulphides 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. For example: sols of metals.
Now, the stability of hydrophilic sols depends on two thingsthe
presence of a charge
and the salvation of colloidal particles. On the other hand, the stability of hydrophobic
sols is only because of the presence of a charge. Therefore, the latter are much less
stable than the former. If the charge of hydrophobic sols is removed (by addition of
electrolytes), then the particles present in them come closer and form aggregates,
leading to precipitation.