The best description of a control group in an experiment is: 1. The control group is identical to each test group except for one variable.
This means that the control group is kept constant while the test groups are altered to observe the effects of the variable being tested. The purpose of having a control group is to establish a baseline that the test groups can be compared against, ensuring that any observed effects in the test groups are due solely to the manipulated variable and not other factors. This is crucial for validating the results of the experiment and drawing accurate conclusions.