On adding a few drops of dilute $HCl$ or $FeCl_3$ to freshly precipitated ferric hydroxide,a red-coloured colloidal solution is obtained. This phenomenon is known as:

Tyndall effect is observed only when:
$(i)$ the diameter of the dispersed particles is not much smaller than the wavelength of the light used.
$(ii)$ the refractive indices of the dispersed phase and the dispersion medium differ greatly in magnitude.
$(iii)$ the size of the particles is generally between $10^{-11} \ m$ and $10^{-9} \ m$ in diameter.
$(iv)$ the dispersed phase and the dispersion medium can be seen separately in the system.

Which of the following compounds has the highest coagulating power for a ferric hydroxide sol?

Which of the following statements is not correct?

The stability of lyophilic colloids is due to

Colloidal gold solutions prepared by different methods have different colors due to: