Which of the following forms a colloidal solution in water?

The coagulation of $200 \ mL$ of a positive colloid took place when $0.73 \ g$ of $HCl$ was added to it without changing the volume much. The flocculation value of $HCl$ for the colloid is

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.

In the precipitation of soap,which can be used instead of $NaCl$?

What happens when gelatin is mixed with a gold sol?

Which of the following is an example of a multi-molecular colloid?