How many spare O2 masks are generally aboard the aircraft?

The correct answer reflects standard aviation safety practices, where typically, two spare oxygen masks are carried aboard the aircraft. This number is generally sufficient to address emergencies that may arise in the cabin for passengers and crew, ensuring that there is an extra mask available for unpredicted situations, such as a medical emergency or the requirement for additional use beyond the standard supply.

Having two spare masks allows for redundancy, which is crucial in emergency situations where time is critical. In the case of rapid decompression or loss of cabin pressure, the availability of spare masks becomes essential, enabling swift action to ensure the safety and well-being of all on board.

The choice of two aligns with regulatory requirements and industry conventions that prioritize passenger safety and efficient emergency response. Therefore, the selection of two as the amount of spare oxygen masks reflects not only compliance with safety regulations but also the operational readiness of the flight crew to manage in-flight emergencies effectively.