According to Hardy Schulze rule, greater the charge on oppositely charged ion, greater is its coagulating power. Since arsenic sulphide is a negatively charged sol, thus, the order of coagulating power is $Na^+ < Ba^{2+} < Al^{3+}$
A colloid is a mixture in which one substance consisting of microscopically dispersed insoluble particles is suspended throughout another substance. Some definitions specify that the particles must be dispersed in a liquid, while others extend the definition to include substances like aerosols and gels.
Example of Colloids:
Blood: A respiration pigment which has albumin protein in water. Pigment part contains albumin that acts as the dispersed phase and the dispersion medium is water. It is a hydrosol.
Cloud: It contains air which is the dispersion medium and droplets of water as a dispersed phase. These are aerosol.
Gold sol: It is a metallic sol in which gold particles are dispersed in the water.
Colloids are insoluble particle mixes (sometimes known as colloidal solutions or colloidal systems). They depict the microscopic dispersion of one substance as well as a suspension in another substance. In a colloid, the size of these suspended particles can range from 1 to 1000 nanometres (10-9 meters). They are heterogeneous in nature.
Colloidal dispersions are made up of particles that are substantially larger than conventional solution solutes. Colloidal particles are large molecules or clusters of smaller species that scatter light.
Purification of Colloids:
Colloids contain ionic impurities and other categories of impure substances that decrease the quality of colloids used in various applications. Following are the methods to purify the colloids.
