Question

When dilute aqueous solution of ${\text{AgN}}{{\text{O}}_{\text{3}}}$ (excess) is added to ${\text{KI}}$ solution, positively charged sol of ${\text{AgI}}$ is formed due to adsorption of:
A. ${\text{NO}}_3^ -$
B. ${\text{O}}_2^ -$
C. ${\text{A}}{{\text{g}}^ + }$
D. ${{\text{K}}^ + }$

Answer 1

The mixture in which one substance is divided into very minute particles is known as a colloid. An aggregate of very fine solid particles dispersed in a fluid is known as a sol. A sol is a type of colloid.

Complete step by step solution:
A positively charged sol means a colloid having positively charged ions on its surface.
We already have ${\text{AgI}}$ molecules in the solution. The ${\text{AgI}}$ molecules will adsorb the common ion present in the solution.
Thus, when dilute aqueous solution of ${\text{AgN}}{{\text{O}}_{\text{3}}}$ (excess) is added the ${\text{AgI}}$ molecules will adsorb the ${\text{A}}{{\text{g}}^ + }$ ions.
When dilute aqueous solution of ${\text{AgN}}{{\text{O}}_{\text{3}}}$ (excess) is added to ${\text{KI}}$ solution, positively charged sol of ${\text{AgI}}$ is formed due to the adsorption of ${\text{A}}{{\text{g}}^ + }$ ions on the surface of ${\text{AgI}}$ molecules.
The reaction is as follows:
${\text{AgN}}{{\text{O}}_{\text{3}}} + {\text{KI}} \to {\text{AgI (Ag}}{{\text{)}}^ + } + {\text{KN}}{{\text{O}}_3}$

**Thus, the correct option is (C) ${\text{A}}{{\text{g}}^ + }$.

Additional Information:**
The colloidal particles possess an electrical charge. The fluid used for dispersion possesses a charge opposite to that of the colloidal particles. Thus, the charges are balanced and the colloidal solution becomes electrically neutral. The stability of colloidal solution depends on the charge possessed by it.
Colloidal solutions have very minute particles and they are not visible by naked eyes.
If the fluid used for dispersion of colloids is water then the sol is known as hydrosol. If the fluid used for dispersion of colloids is air then the sol is known as aerosol.

Note:
Haemoglobin in blood is positively charged. It is inside the red blood cell. The membrane of the red blood cell is negatively charged.
Examples of positively charged sols: Haemoglobin, metal hydroxides, basic dyes, etc.
Examples of negatively charged sols: Metal sols, metal sulphides, gold sols, blood, starch, acidic dyes, etc.