For arsenious sulphide sol,which one of the following salt solutions will be most effective for coagulation?

The size of colloidal particles is . . .

The coagulation of $100 \, mL$ of a colloidal sol of gold is completely prevented by the addition of $0.25 \, g$ of a substance '$X$' to it before adding $10 \, mL$ of $1 \% \ NaCl$ solution. The gold number of '$X$' is:

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 rule that states that the greater the valency of the flocculating ion,the greater is its coagulating power,was proposed by whom?

Butter is a colloid. It is formed when