In coagulation the colloidal solution of As₂S₃, which has the minimum coagulation value ?

AlCl₃

The correct answer is option 4. AlCl₃.

In the process of coagulation, colloidal particles come together and form larger aggregates, leading to the separation of the dispersed phase from the dispersion medium. This aggregation is typically induced by the addition of electrolytes, which neutralize the charges on the colloidal particles and reduce the electrostatic repulsion between them, allowing them to coalesce.

The minimum coagulation value refers to the minimum concentration of an electrolyte required to induce coagulation in a colloidal solution. Different electrolytes have different coagulating powers, depending on factors such as their charge and size.

Among the options provided (\(NaCl\), \(KCl\), \(BaCl_2\), and \(AlCl_3\)), aluminum chloride \((AlCl^3)\) is often known to have a strong coagulating effect on colloidal solutions. This is because aluminum ions \((Al^{3+}\)) have a high charge density and can effectively neutralize the charges on colloidal particles, promoting their aggregation.

Therefore, in the case of the colloidal solution of \(As_2S_3\), which is a common arsenic sulfide colloidal system, aluminum chloride \((AlCl_3)\) is likely to have the minimum coagulation value compared to the other electrolytes listed.