Some substances behave as electrolytes in dilute solutions and as colloids in their concentrated solutions. Their colloidal forms are said to form

What type of colloid is fog?

Tyndall effect is more effectively shown by:

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.

How many of the following are true solutions?
$I :$ Urea solution,
$II :$ Gelatin,
$III :$ Glucose solution,
$IV :$ $NaCl$ solution,
$V :$ Butter,
$VI :$ Blood

Brownian motion arises due to ....