Which of the following is not a property of a sol?

The density of gold is $19 \, g/cm^3$. If $1.9 \times 10^{-4} \, g$ of gold is dispersed in $1 \, L$ of water to form a sol of spherical gold particles of radius $10 \, nm$,find the number of gold particles per $nm^3$ in the sol.

Match column $I$ (process) with column $II$ (application).

Column $I$	Column $II$
$A$. Dialysis	$a$. Cleansing action of soap
$B$. Peptization	$b$. Coagulation
$C$. Emulsification	$c$. Colloidal solution preparation
$D$. Electrophoresis	$d$. Purification of colloidal solution

The correct statements with respect to dialysis of colloidal solution are
$I$. Colloidal particles can pass through the membrane.
$II$. Animal bladder can be used as membrane.
$III$. Cellophane is not used as membrane.
$IV$. Ions or small molecules can diffuse through membrane into water.

$Fe(OH)_3$ is a positively charged sol. For its precipitation, the best precipitating agent is:

Electrophoresis is used