Which of the following nanomaterials has two dimensions less than $100 \ nm$?

Lyophobic colloids are:

When a colloidal solution is observed under a microscope,we can see:

The Tyndall effect is observed only when the following conditions are satisfied $:$
$1$. The diameter of the dispersed particles is much smaller than the wavelength of the light used.
$2$. The diameter of the dispersed particle is not much smaller than the wavelength of the light used.
$3$. The refractive indices of the dispersed phase and dispersion medium are almost similar in magnitude.
$4$. The refractive indices of the dispersed phase and dispersion medium differ greatly in magnitude.

The stability of a lyophobic colloid is due to

Which one of the following sols acts as a lyophilic colloid?