Colloidal solutions cannot be purified by which of the following processes?

Consider the following statements:
Statement-$I$ : Gold sol is prepared by Bredig's arc method.
Statement-$II$ : Bredig's arc method involves both dispersion and condensation.

$A$ sol contains positively charged colloidal particles. Which of the following solutions will require the minimum concentration for its coagulation?

The nature of charge on resulting colloidal particles when $FeCl_3$ is added to excess of hot water is:

The mass of Haemoglobin in $mg$ required to protect from coagulation of $50 \ mL$ of a gold sol on adding $5 \ mL$ of $10 \% NaCl$ solution is: (Gold number of Haemoglobin $= 0.03$)

Under ambient conditions,which among the following surfactants will form micelles in aqueous solution at the lowest molar concentration?