Which of the following are examples of anionic surfactants?

• A. Bacterial Agents
• B. Sorbitan Esters
• C. Acacia
• D. Soaps and Sulfonates

Answer: (D)

Anionic surfactants carry a negative charge on their hydrophilic head, usually from carboxylate or sulfonate groups. This negative charge is the defining feature that makes them ionic and able to form micelles with a negatively charged interface in water.

Soaps are alkali salts of fatty acids, providing a carboxylate head (–COO−) that is negatively charged in solution. Sulfonates have sulfonate head groups (–SO3−), also giving a negative charge. Together, these are classic examples of anionic surfactants.

The other options don’t fit because they don’t inherently have a negatively charged head group: some are not surfactants at all (like a natural gum used as a thickener), and others are nonionic surfactants that lack charge on the head.