**Correct Option: B. Surface tension allows small droplets to maintain a spherical shape despite the force of gravity.** ### 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 the molecules within the liquid, leading to a minimized surface area. This phenomenon causes the liquid to behave as if its surface is covered with a stretched elastic membrane. **Effect of Gravity on Droplets:** When a small droplet of liquid is placed in a gravitational field (like on Earth), gravity exerts a downward force on the droplet. However, due to surface tension, the droplet tends to maintain a shape that minimizes its surface area, which is a sphere. 1. **Spherical Shape Maintenance:** - The spherical shape is the most efficient shape for minimizing surface area for a given volume. This means that, even when gravity pulls down on the droplet, the cohesive forces (due to surface tension) work to keep the droplet as spherical as possible. - The balance between the gravitational force pulling the droplet down and the surface tension trying to maintain its shape results in the droplet remaining spherical, as long as it is small enough. 2. **Small vs. Large Droplets:** - For small droplets, the effect of surface tension is significant compared to the gravitational force. This is why small droplets can remain spherical. - As droplets increase in size, the gravitational force becomes more dominant, and surface tension alone may not be sufficient to maintain a perfect spherical shape. Larger droplets may deform under their own weight, but this is not the case for small droplets. ### Why Other Options Are Incorrect: **A. Surface tension causes the droplet to flatten out completely when in a gravitational field.** - This statement is incorrect because surface tension works to minimize the surface area, which leads to a spherical shape rather than flattening. Flattening would require a significant overcoming of the cohesive forces that surface tension provides. **C. Surface tension has no effect on the shape of a droplet in a gravitational field.** - This option is misleading. Surface tension plays a crucial role in determining the shape of the droplet. Without surface tension, the droplet would not maintain its spherical shape and would instead deform significantly under the influence of gravity. **D. Surface tension causes large droplets to break apart into smaller ones when in a gravitational field.** - While it is true that larger droplets can break apart due to instabilities (like the Rayleigh-Plateau instability), this is not a direct effect of surface tension in the context of maintaining shape under gravity. Instead, it is a result of the balance of forces and the instability that arises when the droplet becomes too large. This statement does not accurately describe the effect of surface tension on small droplets. ### Summary of Key Points: - Surface tension minimizes the surface area of a liquid, leading small droplets to adopt a spherical shape. - In a gravitational field, the cohesive forces from surface tension counteract the downward pull of gravity, allowing small droplets to maintain their shape. - Larger droplets may deform or break apart due to gravitational forces, but this does not apply to small droplets. - Understanding the balance between surface tension and gravitational forces is crucial in predicting the behavior of liquid droplets.