**Correct Option: B. Surface tension causes the droplet to form a spherical shape to minimize surface area.** ### Detailed Explanation: **Understanding Surface Tension:** Surface tension is a physical property of liquids that arises from the cohesive forces between liquid molecules. Molecules at the surface of a liquid experience a net inward force because they are attracted to other liquid molecules below them, but not to the air above. This creates a "skin" on the surface of the liquid, which tends to minimize the surface area of the liquid. **Why Option B is Correct:** 1. **Minimization of Surface Area:** The primary role of surface tension is to minimize the surface area of a liquid. When a droplet of liquid is placed on a solid surface, the cohesive forces between the liquid molecules cause the droplet to adopt a shape that has the least surface area for a given volume. This shape is a sphere. 2. **Spherical Shape:** A sphere has the smallest surface area for a given volume compared to any other shape. Therefore, when surface tension acts on a droplet, it pulls the molecules together, forming a spherical shape. This is why small droplets tend to be round. 3. **Balance of Forces:** In a droplet, the inward force due to surface tension is balanced by the outward pressure from the liquid's weight. This balance results in a stable spherical shape. ### Why the Other Options are Incorrect: **Option A: Surface tension causes the droplet to flatten out completely on the surface.** - **Explanation:** This statement is incorrect because while surface tension does influence the shape of the droplet, it does not cause it to flatten out completely. A droplet will flatten only if the adhesive forces between the liquid and the solid surface are significantly stronger than the cohesive forces within the liquid. In most cases, especially with non-wetting liquids, the droplet retains a more spherical shape. **Option C: Surface tension has no effect on the shape of the droplet on a solid surface.** - **Explanation:** This statement is false because surface tension is a critical factor in determining the shape of the droplet. Without surface tension, the droplet would not maintain its shape and would spread out more on the surface. The cohesive forces that create surface tension are what allow the droplet to maintain its form. **Option D: Surface tension causes the droplet to evaporate more quickly on the surface.** - **Explanation:** This statement is misleading. While surface tension does play a role in the evaporation process, it does not directly cause a droplet to evaporate more quickly. In fact, a droplet with higher surface tension may evaporate more slowly because the cohesive forces keep the molecules together, making it harder for them to escape into the air. Evaporation is more influenced by factors such as temperature, surface area, and air movement. ### Summary of Key Points: - Surface tension minimizes the surface area of a liquid droplet, leading to a spherical shape. - A sphere has the least surface area for a given volume, which is why droplets tend to form this shape. - Cohesive forces within the liquid and adhesive forces with the surface determine the droplet's final shape. - Surface tension does not cause flattening or increased evaporation rates; it primarily influences the droplet's shape. This understanding of surface tension is crucial for various applications in physics and engineering, including fluid dynamics, material science, and even biological systems.