High surface tension
The spherical shape of droplets of mercury is primarily due to its high surface tension. Surface tension is the property of a liquid that allows it to resist external forces and minimize its surface area. It is caused by the cohesive forces between the molecules of the liquid.

Cohesive forces
Mercury is a metal that exists in liquid form at room temperature. It is composed of individual atoms that are held together by strong metallic bonds. These metallic bonds result in high cohesive forces between the mercury atoms.

Spherical shape
When a droplet of mercury is formed, the cohesive forces between the mercury atoms pull the liquid inward, causing the droplet to take on a spherical shape. This is because a sphere has the smallest possible surface area for a given volume, allowing the droplet to minimize its surface energy.

Surface tension and droplet shape
Surface tension is directly related to the droplet's shape. It is the force acting parallel to the surface of the liquid, trying to minimize the surface area. In the case of mercury, the high surface tension pulls the liquid inward, making it form a spherical shape.

Comparison with low surface tension liquids
If the surface tension of a liquid is low, the cohesive forces between its molecules are weaker. As a result, the liquid is less able to resist external forces and maintain a spherical shape. Droplets of low surface tension liquids tend to spread out and form flat or irregular shapes instead.

Other factors
While surface tension is the primary factor determining the shape of mercury droplets, other factors such as gravity and adhesion also play a role. Gravity pulls the droplet downward, but the spherical shape minimizes its effect. Adhesion refers to the attraction between the mercury droplet and the surface it is in contact with. However, the high surface tension of mercury overcomes the adhesive forces, allowing the droplet to maintain its spherical shape.

In conclusion, the spherical shape of droplets of mercury is due to its high surface tension. The cohesive forces between the mercury atoms cause the liquid to pull inward, minimizing the surface area and forming a spherical shape. This is in contrast to liquids with low surface tension, which tend to spread out and form irregular shapes.