Final answer:
A Type I Personal Flotation Device is designed to turn most unconscious people face up in the water, ensuring an open airway, especially in open or rough waters.
Step-by-step explanation:
The type of Personal Flotation Device (PFD) that will turn most unconscious people face up in the water is a Type I PFD. This type is usually bulkier than other PFDs and is designed to turn an unconscious person to a face-up position in the water, which is crucial for ensuring an open airway. It's important to note that while Type I PFDs have the highest buoyancy and are suitable for all waters, specifically open, rough, or remote waters where rescue may take longer, there is still no guarantee of face-up rotation for every individual due to variations in body weight, size, and water conditions.