Whar is the control group

Control group remains unchanged.

Explanation:

For example if you are trying to see if watering plants with Pepsi is better.

Your experiment plant would get watered with Pepsi.

Your control plant would get watered with water. (Control groups serve as a reference to compare in the experiment)

The control group is a group separated from the rest of the experiment such that the independent variable being tested cannot influence the results.