A simple way to form a drop is to allow liquid to flow slowly from the lower end of a vertical tube of small diameter. The surface tension of the liquid causes the liquid to hang from the tube, forming a pendant. When the drop exceeds a certain size it is no longer stable and detaches itself. The falling liquid is also a drop held together by surface tension.

Explanation:

The spherical shape of rain droplets can be explained by the property of water known as surface tension.

Surface Tension:
Surface tension is a property of liquids that arises due to the cohesive forces between its molecules. It is the force acting on the surface of a liquid that tends to minimize the surface area and make it behave like a stretched elastic membrane. Water has a relatively high surface tension compared to other liquids.

Formation of Spherical Shape:
When rain droplets are formed, water molecules at the surface experience a net inward cohesive force due to the surface tension. This force acts equally in all directions, resulting in a net inward force that pulls the water molecules towards the center of the droplet.

This inward force causes the droplet to minimize its surface area and form a spherical shape. A sphere has the smallest surface area for a given volume, making it the most stable shape for a droplet.

Minimization of Surface Area:
The surface tension of water helps in minimizing the surface area of the droplet. The cohesive forces between water molecules cause the droplet to contract and assume a shape that has the smallest possible surface area. This is why rain droplets are spherical in nature.

Importance of Spherical Shape:
The spherical shape of rain droplets is important for various reasons:
1. Aerodynamic Efficiency: The spherical shape allows the droplets to move efficiently through the air, reducing air resistance and increasing their speed of fall.
2. Equal Distribution of Weight: The spherical shape ensures that the weight of the droplet is evenly distributed, preventing any distortion or elongation of the droplet during free fall.
3. Maximizing Collision Efficiency: When rain droplets collide with each other or with other objects, their spherical shape ensures maximum contact and efficient transfer of momentum and energy.

Conclusion:
In conclusion, the surface tension of water is the property that explains the spherical shape of rain droplets. This property allows the droplets to minimize their surface area and assume a shape that is most stable and efficient for their movement through the atmosphere.

B - surface tension.