ANS:D - high surface tension.

The spherical shape of mercury droplets is primarily due to its high surface tension. Surface tension is the property of a liquid that causes its surface to behave like a stretched elastic membrane. It is caused by the cohesive forces between the molecules in the liquid, which tend to minimize the surface area to achieve the lowest energy state. Mercury has one of the highest surface tensions of all liquid elements at room temperature. This high surface tension causes mercury droplets to form into nearly perfect spheres when they are in contact with a surface or other materials. The cohesive forces between mercury molecules are so strong that they pull the droplet into the most compact shape possible, which is a sphere. While mercury also has a relatively high density compared to many other liquids, it is the high surface tension that primarily determines the spherical shape of mercury droplets. Therefore, the spherical shape of mercury droplets is due to its high surface tension.