Light scattering in colloidal particles is

The surface tension of a soap solution is $30 \times 10^{-3} \, N/m$. The work done to increase the surface area of a soap film from $5 \, cm \times 5 \, cm$ to $10 \, cm \times 10 \, cm$ is:

$X$ is a protecting colloid. The following data is obtained for preventing the coagulation of $10 \ mL$ of gold sol to which $1 \ mL$ of $10 \% NaCl$ is added. What is the gold number of '$X$'?

Expt. No.	Weight of $X$ (in $mg$) added to gold sol	Coagulation
$1$	$24$	Not prevented
$2$	$23$	Not prevented
$3$	$26$	prevented
$4$	$27$	prevented
$5$	$25$	prevented

Match List-$I$ with List-$II$ and select the correct option:

List-$I$	List-$II$
$I$. Colloidal antimony	$A$. Kala-azar
$II$. Silver sol	$B$. Intramuscular injection
$III$. Milk of magnesia	$C$. Eye lotion
$IV$. Gold sol	$D$. Stomach disorder

Which of the following is not involved in coagulation?

The reason for exhibiting the Tyndall effect by colloidal particles is