The nurse has recently set limits for a client with borderline personality disorder. The client tells the nurse, 'You used to care about me. I thought you were wonderful. Now I can see that I was mistaken. You are hateful.' This outburst can be assessed as:

The correct answer is C: splitting. Splitting is a defense mechanism commonly seen in individuals with borderline personality disorder where they perceive others as either all good or all bad. In this scenario, the client is idealizing the nurse as wonderful and caring, but when the nurse sets limits, the client quickly shifts to viewing the nurse as hateful. This extreme and sudden change in perception demonstrates splitting. Denial (A) is the refusal to accept reality, separation-individuation (B) refers to the developmental process of establishing a sense of self, and reaction formation (D) involves expressing the opposite of one's true feelings. In this case, the client's behavior is best explained by the defense mechanism of splitting.