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

Among the following methods:
$(i)$ Addition of an electrolyte
$(ii)$ Electrophoresis
$(iii)$ Addition of a protective colloid
$(iv)$ Addition of an oppositely charged sol
the coagulation of a lyophobic sol can be carried out by:

$Sb_2S_3$ sol,$CdS$ sol and Gold sol are examples of:

Colloidal solutions can be purified by

Which of the following electrolytes has the maximum coagulating power?

Select the incorrect statement.