Although molecules in a liquid are electrically neutral in nature, there are often small attractive forces between them. Within a body of a liquid, a molecule will not experience a net force because the forces by the neighboring molecules all cancel out. However for a molecule on the surface of the liquid, there will be a net inward force since there will be no attractive force acting from above the molecule . This inward net force causes the molecules on the surface to contract and to resist being stretched or broken. Thus the surface is under tension and has Surface tension.
Surface tension is the tendency of the surface of a liquid to behave as though covered with a skin.
This is due to the cohesive forces between the molecules at and near the surface.