Which of the following is a scientific hypothesis?

A scientific hypothesis is a statement that can be tested and potentially falsified through experimentation or observation. It presents a clear cause-and-effect relationship that can be examined under controlled conditions.

In this case, the statement that "tides are caused by the Moon" serves as a scientific hypothesis because it suggests a specific relationship where the gravitational pull of the Moon affects ocean water levels, leading to tides. This claim can be tested by observing tide patterns and correlating them with the Moon's position. Numerous studies and observations can be conducted to provide evidence supporting or refuting the idea, making it a robust hypothesis within the realm of science.

The other statements do not present as clear hypotheses or are not as directly testable. For example, while the idea that "tides are caused by the Sun" is also a valid statement, it proposes a different cause and does not specifically address the gravitational effects of the Moon. The statement about Earth's rotation and light and darkness lacks a clear testable mechanism, and the assertion that "chlorophyll is unnecessary for grass color" does not lend itself to straightforward testing about the role of chlorophyll in photosynthesis and plant color.