Final answer:
One variable was tested in Homer's experiment—the type of treatment for the green slime, which was the testable variable. No change was observed after three days, indicating that neither coconut juice nor water had an immediate visible effect.
Step-by-step explanation:
In the scenario described, Homer is experimenting to test the effectiveness of coconut juice in removing green slime from the shower, using water as a control. Only one variable is being tested, which is the type of treatment applied to the slime—coconut juice versus water. The testable variable, in this case, is the substance used to treat the slime to see which one, if any, would cause a change in its appearance. While the result shows no change after three days, the experiment is set up to determine the effectiveness of coconut juice as a cleaning agent compared to plain water.
The format and execution of Homer's experiment resemble a standard scientific approach, where a hypothesis is tested against a control to observe the difference in outcomes. A control is crucial in an experiment as it provides a baseline comparison. However, the lack of change in the green slime suggests that neither treatment had an effect, or additional time or different methods might be needed to assess their effectiveness adequately.