The correct answer is: B. less.
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 of the liquid. The stronger the cohesive forces, the greater the surface tension.
The surface tension of mercury is less than that of water because the cohesive forces between mercury molecules are weaker than those between water molecules. This is because mercury is a metal, while water is a polar molecule. The electrons in a metal are shared equally by all of the atoms in the metal, while the electrons in a polar molecule are shared unequally between the atoms. This difference in electron sharing causes the molecules in a metal to be more strongly attracted to each other than the molecules in a polar molecule.
The size of the glass tube does not affect the surface tension of the liquid inside the tube. The surface tension of a liquid is a property of the liquid itself, and it is not affected by the container that the liquid is in.