The stability of a colloidal dispersion is greatly influenced by the concentration of electrolytes present in the system. Electrolytes are substances that dissociate into ions when dissolved in a solvent, such as water. In a colloidal dispersion, the dispersed particles carry an electric charge, which plays a crucial role in maintaining the stability of the system.The presence of electrolytes in a colloidal dispersion can either stabilize or destabilize the system, depending on the concentration. This phenomenon can be explained by the DLVO Derjaguin, Landau, Verwey, and Overbeek theory, which considers the balance between attractive van der Waals forces and repulsive electrostatic forces between colloidal particles.At low electrolyte concentrations, the repulsive electrostatic forces dominate, preventing the particles from coming close to each other and thus maintaining the stability of the colloidal dispersion. However, as the electrolyte concentration increases, the repulsive forces are reduced due to the screening effect of the counterions ions of opposite charge present in the electrolyte. This allows the attractive van der Waals forces to dominate, leading to particle aggregation and eventually the destabilization of the colloidal dispersion.Experimental evidence supporting this phenomenon can be found in the classic experiment conducted by Schulze and Hardy in 1882, known as the Schulze-Hardy rule. They studied the coagulation destabilization of colloidal gold particles by adding varying concentrations of electrolytes to the dispersion. They observed that the coagulation of the colloidal gold particles occurred at lower electrolyte concentrations when the valency of the counterions was higher.For example, they found that trivalent counterions e.g., Al3+ were much more effective in destabilizing the colloidal gold dispersion than divalent e.g., Ca2+ or monovalent e.g., Na+ counterions. This observation led to the formulation of the Schulze-Hardy rule, which states that the coagulation power of an electrolyte is directly proportional to the sixth power of the valency of the counterion Z^6 .In conclusion, the electrolyte concentration plays a significant role in determining the stability of a colloidal dispersion. At low concentrations, the repulsive electrostatic forces maintain the stability of the system, while at higher concentrations, the attractive van der Waals forces lead to destabilization. The experimental evidence provided by the Schulze-Hardy rule demonstrates the impact of electrolyte concentration and counterion valency on the stability of colloidal dispersions.