Which of the following is NOT a broad category of emulsifiers?

• A. Surfactants, stabilizers, and thickeners
• B. Water-soluble polymers
• C. Proteins functioning as emulsifiers
• D. Solvents

Answer: (D)

Emulsifiers stabilize oil–water mixtures by migrating to the interface and either lowering interfacial tension or forming a protective film that keeps droplets from coalescing. Broad categories include surfactants (surface-active agents that reduce interfacial tension), stabilizers and thickeners (which help prevent droplet movement and coalescence or increase continuous-phase viscosity), water-soluble polymers (which can stabilize emulsions through steric or viscosity effects), and proteins that act as emulsifiers (their amphiphilic nature lets them adsorb at the interface and fortify a stabilizing film). Solvents, however, are liquids used to dissolve components or serve as the phases themselves; they don’t provide interfacial stabilization or a protective film. Therefore, solvents are not a broad category of emulsifiers.