Explanation:

The correct answer is option 'A' - Surface tension.

Surface Tension:
Surface tension is a property of liquids that arises due to the cohesive forces between the molecules at the surface of the liquid. It is the force that acts parallel to the surface and tends to minimize the surface area of a liquid.

Explanation:

When raindrops fall through the atmosphere, they experience resistance from the air. This resistance causes the raindrop to deform slightly, and surface tension tries to minimize the surface area of the droplet. As a result, the raindrop takes on a spherical shape.

Surface tension and spherical shape:
- Surface tension acts in such a way that it minimizes the surface area of a liquid. In the case of a raindrop, surface tension pulls the molecules at the surface of the droplet towards each other, causing the droplet to take on a spherical shape.
- The spherical shape is the most efficient shape for minimizing the surface area of a given volume. A sphere has the smallest surface area for a given volume compared to any other shape.
- Due to the cohesive forces between the water molecules, the surface tension in a raindrop is strong enough to overcome the resistance from the air and pull the droplet into a spherical shape.

Other properties:
- Critical phenomenon: Critical phenomenon refers to the behavior of a substance at its critical point, where its properties change dramatically. This property does not directly explain the spherical shape of rain droplets.
- Viscosity: Viscosity is a measure of a liquid's resistance to flow. While viscosity affects the behavior of liquids, it does not directly explain the spherical shape of rain droplets.
- Pressure: Pressure can affect the size and shape of rain droplets but does not specifically explain the spherical shape. Pressure variations in the atmosphere can cause the droplets to grow or shrink, but the underlying force responsible for the spherical shape is surface tension.

Conclusion:

The spherical shape of rain droplets can be explained by the property of surface tension. Surface tension acts to minimize the surface area of the droplet, resulting in a spherical shape that is the most efficient for minimizing surface area.