Final answer:
The correct response is to inform the sister that a patient's chart is private and confidential, and that such information cannot be shared without the patient’s consent due to regulations like HIPAA.
Step-by-step explanation:
The best response by the nurse when a patient's sister asks to read the patient's chart is b. Respond that the contents of a patient's chart are private and confidential. Patient privacy is protected by regulations such as the Health Insurance Portability and Accountability Act (HIPAA) in the United States, which prohibits sharing personal health information without the patient's consent. It's important for healthcare providers to maintain these confidentiality standards unless the patient has given explicit permission for specific individuals to view their medical records.