Final answer:
X-ray confirmation is the most accurate method for determining the proper placement of a nasogastric tube, as it visually ensures correct placement within the stomach.
Step-by-step explanation:
The most accurate determination of proper placement of a nasogastric tube is x-ray confirmation. While assessment of the patient's heart rate through auscultation using a stethoscope is a valuable tool for evaluating heart health, it does not guarantee the correct placement of a nasogastric tube. Similarly, blood pressure measurement and respiratory rate assessment are important vital signs but do not specifically confirm the placement of the nasogastric tube. To ensure that the tube has been placed in the stomach and not in the lungs or esophagus, which can have serious complications, an x-ray is taken after tube placement.