Participants in an experiment on stress management are given stress reduction techniques and then measured for the effect. what is the role of the control group in this experiment?

They receive no techniques at all, but they are measured.

Explanation:

When the effect of a treatment is to be studied, participants are divided into two groups. One group receives the treatment while the other group does not.

The group which receives the treatment should show the claimed effects of the treatment while the other group should not show the effects. The group which does not receive the treatment is called the control group

Here, the control group will not be administered any techniques at all but their state will be measured.