Final answer:
The most appropriate question for a nurse to ask a patient to assist in establishing a nursing diagnosis of Diarrhea would be option b. "How many bowel movements a day have you had?"
Step-by-step explanation:
The most appropriate question for a nurse to ask a patient to assist in establishing a nursing diagnosis of Diarrhea would be option b. "How many bowel movements a day have you had?" This question helps to determine the frequency of bowel movements and can help in identifying if the patient is experiencing excessive or abnormal bowel movements.