What are the required checks for the Scott POB during a preflight inspection?

The correct answer pertains to the necessity of having the gauge reading above 1500 PSI while ensuring that the mask is attached to both the HI and LO valves during the preflight inspection of the Scott Portable Oxygen Bottle (POB). A reading above 1500 PSI indicates that the oxygen bottle is adequately pressurized and ready for use in case of an emergency.

Attaching the mask to the HI and LO valves ensures that the bottle can provide oxygen effectively. This set-up allows for a proper check of the system as both configurations are necessary for delivering oxygen at different flow rates, ensuring that the equipment is functional during a potential inflight emergency.

In the other options, there are various shortcomings: having the gauge below 1500 PSI, having a reading above 1000 PSI, or removing the mask from the valve. These conditions do not meet the established safety requirements for preflight inspections, as they may imply that the oxygen bottle is either out of service or not fully prepared for emergencies. This makes option B the only appropriate choice for ensuring safety standards are upheld.