Psychologists are required to debrief subjects thoroughly after a research study when the

The correct answer that "deceives subjects about the true purpose of the research."
Sometimes, the subjects used in the research may encounter confusion due to the study, wherein what they find and discover throughout the process of the study may cause them to become confused of the true meaning and purpose of the study, which is why psychologists are required to debrief their subjects when they get tied up in these kind of events.