Why can a water strider walk on the surface of the water and not sink?

A water strider can walk on the surface of the water primarily due to surface tension. Surface tension is a physical property that arises from the cohesive forces between water molecules at the surface. These molecules are attracted more strongly to each other than to the air above them, creating a 'film' that resists external force.

The water strider's legs are adapted to spread its weight over a larger area, which enhances the effect of surface tension and allows it to remain on the water’s surface without breaking through. This adaptation effectively counters the force of gravity acting on the insect's body, preventing it from sinking.

Other factors listed, such as high viscosity, density of water, and air pressure, do not adequately explain why the water strider can walk on water. While water's density and viscosity can influence fluid behavior, it is the cohesive forces at the surface (surface tension) that enable the water strider to utilize that property for locomotion across the water’s surface.