What happens when a surfactant is added to water in terms of surface tension?

• A. It decreases surface tension, allowing the liquid to spread.
• B. It increases surface tension, reducing spreading.
• C. It neutralizes pH.
• D. It changes the liquid’s color.

Answer: (A)

Surfactants lower the surface tension of water. They have a hydrophobic tail and a hydrophilic head and migrate to the air–water interface, where they orient themselves to disrupt the water’s cohesive forces at the surface. This reduces surface tension, allowing the liquid to spread and wet surfaces more easily. The other effects listed—neutralizing pH or changing color—aren’t typical outcomes of adding a surfactant to water, so they don’t describe what happens to surface tension.