In an experiment, what is the purpose of a control group?

• A. To receive the experimental treatment.
• B. To provide a baseline for comparison.
• C. To eliminate all variables.
• D. To guarantee a positive result.

Answer: (B)

The main idea here is that a control group provides a baseline to compare against the group that receives the treatment. By keeping all conditions the same except for the independent variable, the control group shows what happens without the treatment, so any observed differences can be attributed to the treatment itself. The control group does not receive the experimental treatment—that’s what the experimental group does. You can’t eliminate all variables in practice, though you try to hold as many constant as possible to reduce confounding factors. And a control group doesn’t guarantee a positive result; it just helps you interpret what the treatment did.