Alum helps in purifying water by

Explain what is observed:
$(i)$ When a beam of light is passed through a colloidal sol.
$(ii)$ An electrolyte,$NaCl$,is added to hydrated ferric oxide sol.
$(iii)$ Electric current is passed through a colloidal sol.

Which of the following is an example of multimolecular colloids?

Jelly is a colloidal solution of

The qualitative sketches $I$,$II$,and $III$ given below show the variation of surface tension with molar concentration of three different aqueous solutions of $KCl$,$CH_3OH$,and $CH_3(CH_2)_{11}OSO_3^{-}Na^{+}$ at room temperature. The correct assignment of the sketches is

Give information about Brownian movement.