Answer the question on the basis of passage given below:

A colloid is a heterogenous system in which a substance is dispersed (dispersed phase) as fine particles in another substance called dispersion medium. Their particle size is intermediate between that of pure solutions (<1 nm) and suspension (>1000 nm).

They are known for interesting properties such as enormous surface area, Tyndall effect, Brownian Motion etc. They are widely used in industries and day to day life. Some prominent uses of colloids are those in smoke precipitators, purification of water, medicines cleansers etc.

Which of the following electrolyte exhibits maximum flocculating power in the coagulation of a positive metal hydroxide sol?

$K_4[Fe(CN)_6]$

The correct answer is Option (4) → $K_4[Fe(CN)_6]$.

The electrolyte that exhibits the maximum flocculating power in the coagulation of a positive metal hydroxide sol is: \(K_4[Fe(CN)_6]\).

The flocculating power of an electrolyte depends on the charge on the ions, as explained by the Hardy-Schulze rule. According to this rule, the greater the charge on the oppositely charged ion of the electrolyte, the greater its ability to cause coagulation of the colloid.

In the case of a positive metal hydroxide sol, the sol particles are positively charged. Therefore, we need an electrolyte that provides anions with a high negative charge for effective coagulation. The flocculating power increases with the charge of the anion. Let us look at the anions in the given options:

\(KCl\) provides \(Cl^-\) (monovalent anion, -1 charge).

\(K_2SO_4\) provides \(SO_4^{2-}\) (divalent anion, -2 charge).

\(K_3PO_4\) provides \(PO_4^{3-}\_) (trivalent anion, -3 charge).

\(K_4[Fe(CN)_6]\) provides \([Fe(CN)_6]^{4-}\) (tetravalent anion, -4 charge).

According to the Hardy-Schulze rule, higher-charged anions have greater flocculating power. Since \([Fe(CN)_6]^{4-}\) has the highest negative charge (-4), it will exhibit the maximum flocculating power.

Conclusion:

\(K_4[Fe(CN)_6]\)will have the maximum flocculating power in the coagulation of a positive metal hydroxide sol due to the presence of the tetravalent \([Fe(CN)_6]^{4-}\) anion.