The gold numbers of protective colloids $A, B, C$,and $D$ are $0.04, 0.004, 10$,and $40$ respectively. The order of their protective power is:

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.

What type of colloid is fog?

Peptization denotes

At isoelectric point:

$20 \ mL$ of $0.5 \ M \ NaCl$ is required to coagulate $200 \ mL$ of $As_2S_3$ sol in $2$ hours. The coagulating value of $NaCl$ is $...........$.