Choose the correct answer from the options given below:

(A) and (C) only

The correct answer is Option 1. (A) and (C) only

Let us break down the charge characteristics of each sol (colloidal dispersion) and clarify why (A) Blood and (C) Gum are correctly identified with a negative charge

A. Blood:

Blood is a complex colloidal system consisting of various components like proteins (e.g., albumin, globulins), cells (e.g., red blood cells, white blood cells), and other substances. Blood components, particularly proteins, typically carry a net negative charge. This negative charge is due to the ionization of acidic side chains in proteins and the presence of negatively charged molecules like phosphate and sulfate groups. Proteins in blood are stabilized by their negative charges which interact with the aqueous environment and maintain blood's colloidal nature.

B. Congo Red:

Congo Red is a synthetic dye used in biological staining and can form a colloidal dispersion in water. Congo Red typically exhibits a negative charge in its colloidal form. The dye molecules contain sulfonic acid groups, which dissociate to give a negative charge in aqueous solutions. The negative charge on Congo Red helps it to interact with positively charged sites in tissues or other substrates during staining.

C. Gum:

Gum, such as gum arabic, is a natural polysaccharide that forms colloidal solutions. Gums usually have a negative charge. This is because they contain acidic groups like carboxyl groups which can ionize to give a negative charge. The negative charge helps to stabilize the colloidal suspension by repelling other similarly charged particles and preventing coagulation or flocculation.

D.Gold Sol:

Gold sol consists of gold nanoparticles dispersed in water. Gold sol typically carries a positive charge. This is due to the stabilization of gold nanoparticles by positively charged ions or surfactants that adsorb onto the surface of the particles. The positive charge on gold nanoparticles helps in stabilization by electrostatic repulsion, preventing the particles from aggregating.

E.Fe(OH)₃ Sol:

Ferric hydroxide forms a colloidal dispersion in water. \(Fe(OH)_3\) sol generally has a negative charge. This is due to the formation of hydroxy ions \((OH^-)\) on the surface of \(Fe(OH)_3\) particles, which imparts a negative charge to the colloid. The negative charge on Fe(OH)₃ particles helps in maintaining the stability of the colloid by electrostatic repulsion.

The correct pairs where the charge of the sol is negative are: Blood (A) and Gum (C), both of which exhibit a negative charge in their colloidal forms.

Thus, Option 1: (A) and (C) only is accurate because both blood and gum typically show a negative charge.