Which of the following substances is not useful in forming a lyophilic sol?

Colloidal solutions of metals like gold,silver and platinum are generally prepared by using

$100 \ mL$ of $0.0018\%(w/v)$ solution of $Cl^{-}$ ion was the minimum concentration of $Cl^{-}$ required to precipitate a negative sol in one $h$. The coagulating value of $Cl^{-}$ ion is $.......$ (Nearest integer).

The coagulation of $200 \ mL$ of a positive colloid took place when $0.73 \ g$ of $HCl$ was added to it. The flocculation value of $HCl$ for the colloid is

$A$ peptising agent is

$A$ liquid aerosol is a colloidal system of