Surface tension is the force that acts on the surface of a liquid, tending to minimize the surface area. It is caused by the cohesive forces between the molecules of the liquid. The stronger the cohesive forces, the higher the surface tension.

Mercury has the highest surface tension of all the liquids listed. This is because the atoms of mercury are very close together, and they have a strong attraction for each other. This strong cohesive force results in a high surface tension.