Identify the negatively charged sol from following.

The charge on colloidal particles arises from preferential ion adsorption, electron capture during electro-dispersion, or dissociation of surface molecules.

Colloidal sols exhibit either positive or negative net charges:

Negatively charged sols: Metal sulfides ($As_2S_3$, $CdS$), acidic dyes (Eosin, Congo red), starch, gum, clay, charcoal, and metals ($Au$, $Ag$, $Pt$).

Positively charged sols: Metal hydroxides ($Fe(OH)_3$, $Al(OH)_3$), basic dyes (Methylene blue), and haemoglobin under specific pH conditions.

Analyzing the options: Eosin is an acidic dye with deprotonated groups, yielding negative charges. Titanium oxide ($TiO_2$) typically adsorbs positive ions. Methylene blue, a basic dye, protonates to form positive charges. Haemoglobin, being amphoteric, varies with pH but is often positive in acidic conditions.

Eosin definitively forms a negatively charged sol.