Which class of chemicals reduces molecular cohesion of a liquid and thereby enables it to flow through smaller openings?

• A. Penetrating agents.
• B. Surfactants.
• C. Catalysts.
• D. Emulsifiers.

Answer: (B)

Surfactants are surface-active substances that insert themselves at interfaces and reduce the cohesive forces holding liquid molecules together, effectively lowering surface tension. With lower surface tension, the liquid wets surfaces more readily and can be driven through small openings or pores more easily, because less energy is needed to create new surface as the liquid advances. The other options don’t address this combination of reducing cohesion within the liquid to promote flow: penetrating agents break down barriers to passage, catalysts speed up chemical reactions, and emulsifiers stabilize mixtures of immiscible liquids rather than promote flow through tiny openings.