Which sol is used as an intramuscular injection?

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.

Which of the following is a water-in-oil $(W/O)$ type of emulsion?

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

$1$. Expt. No.	$2$. Wt (in mg) of $A$ added to gold sol	$3$. Coagulation
$1$	$40$	Prevented
$2$	$35$	Prevented
$3$	$25$	Not prevented
$4$	$32$	Not prevented
$5$	$33$	Prevented

Match List-$I$ with List-$II$.

List-$I$	List-$II$
$A$. Negatively charged sol	$I$. $Fe_{2}O_{3} \cdot xH_{2}O$
$B$. Macromolecular colloid	$II$. $CdS$ sol
$C$. Positively charged sol	$III$. Starch
$D$. Cheese	$IV$. $A$ gel

Choose the correct answer from the options given below:

Which of the following is most active in coagulating $Fe(OH)_3$ sol,if the sol is made by hydrolysis of $FeCl_3$?