Which of the following is an example of multimolecular colloids?

The purple of Cassius is due to the presence of $......$.

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 has the minimum coagulating power?

Assertion : Aqueous gold colloidal solution is red in colour.
Reason : The colour arises due to scattering of light by colloidal gold particles.

The ability of an ion to bring about coagulation of a given colloid depends upon