$A$ 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

Give information about the applications of colloids.

Which one of the following is used in the hardening of leather?

Given below are two statements: one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R)$.
Assertion $(A)$: Dissolved substances can be removed from a colloidal solution by diffusion through a parchment paper.
Reason $(R)$: Particles in a true solution cannot pass through parchment paper but the colloidal particles can pass through the parchment paper.
In the light of the above statements,choose the correct answer from the options given below.

Under ambient conditions,which among the following surfactants will form micelles in aqueous solution at the lowest molar concentration?

Why does bleeding stop by rubbing moist alum?