What type of tube is provided to maintain buoyancy in an inflatable PFD?

The correct choice is the sealed buoyancy tube. In inflatable personal flotation devices (PFDs), the sealed buoyancy tube is designed to hold air and maintain buoyancy when the PFD is inflated. This type of tube ensures that the air remains contained within a durable outer material, providing reliable and sustained buoyancy when needed.

The design of a sealed buoyancy tube prevents air from escaping, thus maintaining the necessary flotation support for the user in the water. This characteristic is vital for ensuring the safety and effectiveness of the PFD during use. Moreover, sealed buoyancy tubes are tested to withstand various conditions and pressures, which is essential for the safety of the diver or swimmer wearing the PFD.

In contrast, the other options reference concepts that do not specifically describe how buoyancy is maintained in inflatable PFDs. Manual inflation tubes are used to inflate a PFD but do not contribute to buoyancy themselves. An air retention tube may sound relevant but is not a standard term widely recognized in relation to PFD design. A compressed gas tube refers to a mechanism that might provide inflation but would not typically be characterized as a primary component for buoyancy retention.