Hydrophilic sols are .......

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?

Colour is imparted to glass by mixing

Among the electrolytes $Na_2SO_4$,$CaCl_2$,$Al_2(SO_4)_3$,and $NH_4Cl$,the most effective coagulating agent for $Sb_2S_3$ sol is

When sugar is added to a colloidal solution,it brings about:

Gold numbers of protective colloids $A, B, C$ and $D$ are $0.50, 0.01, 0.10$ and $0.005$,respectively. The correct order of their protective powers is