Final answer:
The most appropriate response from a manic client in the termination process would be rationalizing the termination and accepting that everything comes to an end.
Step-by-step explanation:
When terminating the nurse-client relationship with a manic client in the psychiatric unit, the most appropriate response from the client would be 4. Rationalizing the termination, saying that 'everything comes to an end.' This response demonstrates an understanding of the termination process and acceptance of the nurse-client relationship ending. The client expressing feelings of anxiety, displaying anger, or withdrawing in silence may indicate unresolved issues or difficulties adjusting to the termination.