Question

Which of the following electrolytes will not be most effective in the coagulation of gold sol?

• A. $NaN{O}_3$
• B. $K_4\left[Fe\right(CN{)}_6]$
• C. $N{a}_{3}P{O}_4$
• D. $MgC{l}_2$

Answer 1

Answer: (A), (B), (C)

The correct options are
A $NaN{O}_3$
B $K_4\left[Fe\right(CN{)}_6]$
C $N{a}_{3}P{O}_4$

Coagulation is the process by which a colloid precipitates out of a solution. The precipitation is brought about by induced aggregation.
The purpose of coagulation is to make solid, suspended colloidal particles thick. This is done by adding sufficient amount of a cationic coagulant. It helps inneutralization of the suspended particles.
Na loses one electron but Mg loses two electrons. So, Mg is strong cation. So, $MgC{l}_2$ is used for the coagulation of gold sol.