For first and second part, refer to Section. The stability of hydrophobic sol is only due to the presence of charge on the colloidal particles. If carge is removed, by addition of suitable electrolytes, the particles will come nearer to each other to form aggregate, i.e., they will coagulate and settle down. On the other hand, the stability of hydrophilic sol is due to charge as well as solvation of the colloidal particles. Both the factors have to be removed to bring about their coagulation.
