To solve this problem, we need to understand the concept of zeta potential in colloidal solutions.$\\$Zeta potential is a measure of the electric potential at the slipping plane of a colloidal particle.$\\$It is an important indicator of the stability of colloidal dispersions.$\\$Here's how zeta potential relates to the stability of colloidal particles:$\\$• Colloidal particles are typically charged, and this charge creates an electric double layer around each particle.$\\$• The zeta potential is the potential difference between the dispersion medium and the stationary layer of fluid attached to the dispersed particle.$\\$• A high zeta potential (either positive or negative) indicates that the particles will repel each other, preventing aggregation.$\\$• Low zeta potential means that the particles are more likely to come together and form aggregates, leading to instability.$\\$Therefore, measuring the zeta potential helps in determining the stability of colloidal particles.$\\$Given the options:$\\$Option 1: Solubility$\\$Option 2: Stability of the colloidal particles$\\$Option 3: Size of the colloidal particles$\\$Option 4: Viscosity$\\$The correct option is 2: Stability of the colloidal particles.$\\$Thus, measuring zeta potential is useful in determining the stability of colloidal particles.