Surface tension arises because
a) The thermodynamic standard state conditions prevent the molecules at the top of the liquid from moving around easily so that they form a "skin" and a bug can walk on it
b) Intermolecular forces are stronger at the surface of a liquid than in the bulk of the liquid.
c) The suspension of a homogeneous mixture of molecules creates resistance to spreading out of the liquid, thereby increasing its surface area.
d) A representation showing specific connections between atoms in a molecule is stronger at the surface from elementary thermodynamics.
e) The dissociation of the substance, useful in interpreting colligative properties, is stronger at the surface of a liquid, which prevents the molecules from breaking down so that a bug can walk on it.