Which principle is applicable in the purification of water using alum?

Consider the following statements related to colloids.
$(I)$ Lyophobic colloids are not formed by simple mixing of dispersed phase and dispersion medium.
$(II)$ For emulsions,both the dispersed phase and the dispersion medium are liquid.
$(III)$ Micelles are produced by dissolving a surfactant in any solvent at any temperature.
$(IV)$ Tyndall effect can be observed from a colloidal solution with dispersed phase having the same refractive index as that of the dispersion medium.
The option with the correct set of statements is

Milk is a colloidal sol of ........

What type of reaction is used to obtain $Au$ (sol)?
Reaction: $2AuCl_3 + 3HCHO + 3H_2O \rightarrow 2Au (sol) + 3HCOOH + 6HCl$

On addition of $1 \, mL$ of $10 \% \, NaCl$ solution to $10 \, mL$ gold sol in the presence of $0.025 \, g$ of starch,the coagulation is just prevented. The gold number of starch is:

The flocculation value of $HCl$ for arsenic sulphide sol is $30 \; mmol \; L^{-1}$. If $H_{2}SO_{4}$ is used for the flocculation of arsenic sulphide,the amount,in grams,of $H_{2}SO_{4}$ in $250 \; mL$ required for the above purpose is (molecular mass of $H_{2}SO_{4} = 98 \; g/mol$)