Which term describes the elastic-like force at the surface of a liquid?

The term that describes the elastic-like force at the surface of a liquid is surface tension. Surface tension occurs due to cohesive forces between liquid molecules; these molecules are attracted to each other, leading to a minimized surface area. This phenomenon allows the surface of a liquid to behave somewhat like a stretched elastic membrane.

Surface tension is what enables small objects, like a paper clip or a water strider insect, to rest on the surface of water without sinking, as the cohesive forces create a "skin" effect. It plays an important role in various applications, including bubble formation, the shape of liquid droplets, and even the movement of liquids through small spaces.

Viscosity, on the other hand, measures a fluid's resistance to flow and does not directly pertain to the surface forces at a liquid's boundary. Capillarity relates to the movement of liquid within narrow spaces due to adhesion and cohesion but is also not the force experienced at the liquid's surface. Density, which refers to mass per unit volume, is a different physical property that does not encompass the surface effects of liquids.