To assess the patient's current mental status, the most appropriate question to ask the patient would be b. "How is your self-image?".
This question helps to get an understanding of how the patient views themselves, which can reveal a lot about their current state of mind.
Asking a general question like "Are you sad?" could be too vague and may not yield an accurate answer, while asking about the patient's breakfast could not provide insight into their current mental status. Asking about their self-image allows the nurse to gain important information and assess the patient's current mental state.