What is the duration for which gaseous oxygen lasts in a B787 flight deck?

The correct answer regarding the duration for which gaseous oxygen lasts in a B787 flight deck is 60 minutes. On a B787, the flight deck is equipped with gaseous oxygen systems that are designed to provide adequate oxygen supply to crew members in case of an emergency, such as cabin depressurization.

Having a supply that lasts approximately 60 minutes allows for adequate response time and management of the situation, ensuring the crew can maintain function and communicate effectively with air traffic control and perform necessary procedures. This duration is based on the expected needs during an emergency scenario, giving the flight crew sufficient time to descend to a safer altitude where supplemental oxygen may no longer be necessary.

The other options represent durations that are either too short or too long for the equipment's intended use, which could compromise safety during critical moments in an emergency situation. The 60-minute duration strikes a balance between providing a sufficient supply while considering the operational requirements of the aircraft and crew.