Surfactants remove oils and dirt by which molecular action?

• A. Lifting off oils and dirt into the water
• B. Dissolving oils into the air
• C. Absorbing moisture from the scalp
• D. Creating a protective film on hair

Answer: (A)

Surfactants work by lifting oils and dirt into the water through emulsification. They have a hydrophobic tail that loves oils and a hydrophilic head that loves water. When mixed with water, they gather at oil–water interfaces and reduce surface tension, so oils and dirt detach from the hair. They then form micelles, tiny spheres where the oil and dirt are trapped inside the nonpolar interior and the water-loving heads face outward toward the water. This structure allows the whole oil/dirt-containing micelle to be rinsed away, effectively removing substances from the hair. The other ideas don’t fit: dissolving oils into the air isn’t how shampoos work, absorbing moisture from the scalp isn’t a cleaning action, and creating a protective film would actually help keep residue on rather than remove it.