Final answer:
The most appropriate response is to inform the client that the doctor has prescribed a lower dose, and this is why the metoprolol tablet is halved.
Step-by-step explanation:
The best response by the nurse when a client questions why their metoprolol tablet has been cut in half is: "The doctor prescribed a lower dose for you." This answer appropriately addresses the client's concern and provides a clear and factual explanation. It also indicates that the nurse is following doctor's orders, which are based on the client's current health status and drug dosage requirement. If the client requires more information or clarification, the nurse can always offer to involve the doctor in the discussion.