Which statement best defines a hypothesis?

A hypothesis is best defined as a testable prediction. In scientific inquiry, a hypothesis provides a starting point for investigation. It formulates an expected outcome based on prior knowledge and observations about the world. This allows scientists to design experiments or studies that can confirm or refute the hypothesis through observable and measurable evidence.

For example, if a researcher proposes that a certain fertilizer will increase plant growth, this can be tested by conducting controlled experiments to measure plant growth under conditions with and without the fertilizer. The ability to test the hypothesis is fundamental to the scientific method, distinguishing it from mere speculation or opinion.

In contrast, the other options provided do not capture the essence of a hypothesis. A conclusion based on experimental data refers to the results obtained after conducting an experiment, which is distinctly different from the initial prediction. A well-established scientific fact implies a level of acceptance and validation that goes beyond the hypothesis stage. Lastly, an untestable idea does not qualify as a hypothesis, as the primary characteristic of a hypothesis is that it must be capable of being tested through experimentation or observation.