Which of the following is an example of a defense mechanism according to Freud's psychoanalytic theory?

Regression is an example of a defense mechanism in Freud's psychoanalytic theory because it involves reverting to an earlier stage of development in response to stress or anxiety. This can manifest in behaviors such as a child who, feeling overwhelmed by a new sibling, may start to suck their thumb or demand attention through tantrums, behaviors typical of a younger child. Freud proposed that such mechanisms serve to protect the individual from uncomfortable emotions or thoughts by acting in ways that alleviate stress.

Defense mechanisms, including regression, operate unconsciously and help individuals cope with reality and maintain self-image when faced with challenging situations. In contrast, the other options listed—cooperation, calmness, and rationalization—do not represent regression's characteristic retreat to earlier behaviors. While rationalization can also be considered a defense mechanism, it involves justifying behaviors or feelings rather than regressing to a less mature state.