In survey based research in Social Sciences, when you decide to tell participants something false about the purpose of the research, you are using

Deliberately telling participants something false about the study's purpose is active deception.

Active deception is deception by commission, planting a misleading account.

Dehoaxing is the debriefing that later corrects such false beliefs, not the deception itself.

Naturalistic observation studies behaviour in its natural setting without manipulation or lies.

Sensitization refers to heightened participant awareness, not misleading them about purpose.

Passive deception, by contrast, misleads by omission through withholding information.