For coagulation ml ferric hydroxide solution, ml of $0.5M$ \[KCl\] is required. What is the coagulation value of \[KCl\]?
A) $5$
B) $10$
C) $100$
D) None of these

Hint: We have to know that the potassium ferrocyanide ion is having the maximum valency hence it will act as the best coagulating agent for ferric hydroxide sol. Ferric hydroxide is a positive sol, thus coagulated by negative ions (like $B{r^ - }$, $SO_4^ - $, $CrO_4^{2 - }$ and ${\left[ {Fe{{\left( {CN} \right)}_6}} \right]^{3 - }}$ -). More is the valency
of negative ions, more is the coagulating power.

Complete answer:
We need to remember that ferric hydroxide is a positively charged colloidal solution. It coagulates negatively charged particles. Higher the negative charge more effectively is the coagulation. The minimum concentration of an electrolyte which is required to cause coagulation is known as coagulating value of sol. It is usually expressed in terms of milli-moles per litre.
Number of millimoles required is the electrolyte solution divided by the volume of colloidal solution (in litres) which is:
\[ = \dfrac{{10 \times 0.5}}{{50}} \times 1000\]
On simplification we get,
\[ = 100\]
So we can say that the coagulation value of \[KCl\] is $100$.
We need to remember that the coagulation occurs as the proteins in your blood called fibrins work with small blood cell fragments called platelets, to form the clot. This is called coagulation, a process that helps the body when an injury occurs because it slows blood loss which acquired the excessive blood clotting that was triggered by another disease or condition.

Hence, the correct answer is option C.

Note:
As we know that inorganic coagulants can be: Aluminum Sulfate (Alum) – One of the most commonly used water treatment chemicals in the world. Alum is manufactured as a liquid, from which the crystalline form is dehydrated. Coagulation power is inversely proportional to coagulation value.