Final answer:
The scenario where a student consumes a sundae but has no memory of it, refers to repression, a defense mechanism where overwhelming memories are blocked from consciousness to avoid stress. The correct option is (A).
Step-by-step explanation:
The scenario posed in the question hints at the psychological phenomenon known as repression, which is a defense mechanism. In this situation, the consumption of an extra-large sundae is forgotten or blocked from conscious memory.
Repression involves involuntarily blocking unpleasant feelings, experiences, or memories from one's conscious mind. This can be compared to turning up the radio to drown out the noise of a car that needs repairs and then forgetting about the problem.
In psychology, repression is similar in the sense that the mind pushes away overwhelming thoughts or memories to avoid addressing the associated stress or anxiety, as originally theorized by Freud in 1920.