Intensity of the scattered light depends upon the difference of which of the following property of the dispersed phase and the dispersion medium?

refractive indices

The correct answer is option 4. refractive indices.

The intensity of the scattered light in a colloidal mixture primarily depends on the difference in the refractive indices between the dispersed phase and the dispersion medium. This is because the scattering of light, as described by the Tyndall effect, occurs due to the interaction of light with the particles in the colloid, which is influenced by the refractive index contrast.

Here is a detailed explanation:

1. Densities: While the density difference between the dispersed phase and the dispersion medium affects sedimentation and stability of the colloid, it does not directly influence the scattering of light.

2. Viscosities: The viscosity of the medium affects the movement and diffusion of colloidal particles but does not directly affect the scattering intensity.

3. Surface tension: Surface tension is relevant to the formation and stability of colloids, especially in emulsions and foams, but it does not directly influence the scattering of light.

4. Refractive indices: The refractive index measures how much light is bent, or refracted, when entering a material. The difference in refractive indices between the dispersed phase (colloidal particles) and the dispersion medium determines the degree of light scattering. A larger difference in refractive indices results in more intense scattering.

Therefore, the correct answer is option 4. Refractive indices.