Question

Why do surfactants lower surface tension?

Answer 1

Because there angle of contact cos is less

Answer 2

$\huge \fbox \purple{Answer}$

The reason for the reduction in the surface tension when surfactant molecules adsorb at the water surface is that the surfactant molecules replace some of the water molecules in the surface and the forces of attraction between surfactant and water molecules are less than those between two water molecules, hence the surfactants lower surface tension