Which of the following statements is not correct for lyophilic sols?

Colloids can be purified by

Identify the correct statement regarding lyophilic colloids from the following.

On adding $AgNO_3$ solution into $KI$ solution,a negatively charged colloidal sol is obtained when they are in:

Fog is a dispersion of

Consider the following statements about the Tyndall effect:
$(I)$ It is used to distinguish between a true solution and a colloidal solution.
$(II)$ It is possible only when the refractive indices of the dispersed phase and the dispersion medium differ significantly.
$(III)$ It is observed only when the size of the colloidal particles is much smaller than the wavelength of the light used.
Which of the following statements are correct?