Match the following types of colloidal systems in List-$I$ with their corresponding names in List-$II$.

List-$I$	List-$II$
$(A)$ Solid dispersed in liquid	$(I)$ Emulsion
$(B)$ Liquid dispersed in liquid	$(II)$ Foam
$(C)$ Gas dispersed in liquid	$(III)$ Gel
$(D)$ Liquid dispersed in solid	$(IV)$ Sol
	$(V)$ Aerosol

The Tyndall effect would be observed in a

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.

What is the potential difference between the fixed layer and the diffused layer of opposite charges called?

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: Finest gold is red in colour,as the size of the particles increases,it appears purple then blue and finally gold.
Assertion $R$: The colour of the colloidal solution depends on the wavelength of light scattered by the dispersed particles.
In the light of the above statements,choose the most appropriate answer from the options given below:

Which one of the following is not a surfactant?