The correct answer is: C. is a function of the curvature of the interface.
Surface tension is the tendency of a liquid surface to shrink into the smallest possible area. It is caused by the cohesive forces between the molecules in the liquid. These forces are stronger at the surface of the liquid than they are within the liquid, because there are fewer molecules on the surface to experience these forces. This difference in force creates a net inward force on the surface of the liquid, which causes it to contract.
The curvature of the interface affects the surface tension because it affects the number of molecules per unit area at the surface. The more curved the interface, the fewer molecules there are per unit area, and the stronger the surface tension. This is why water droplets are spherical, because the sphere is the shape with the smallest surface area for a given volume.
Options A, B, and D are incorrect. Option A is incorrect because surface tension acts perpendicular to the surface, not in the plane of the interface. Option B is incorrect because capillarity is the ability of a liquid to rise or fall in a narrow tube, and it is not the same as surface tension. Option D is incorrect because surface tension increases with fall in temperature.