What indicates that the emergency oxygen cylinder is sufficiently charged for flight?

The correct answer is based on the specific pressure range that indicates a fully charged emergency oxygen cylinder. A contents gauge pointer that falls within the black band between 1800 - 2500 psi signifies that the tank is sufficiently charged for flight operations and can supply the necessary oxygen in an emergency situation.

The choice representing a pressure above 2500 psi suggests that the cylinder is overcharged, which can be a concern as it might exceed safe operational limits, possibly damaging the equipment. Conversely, a contents gauge pointer below 1800 psi indicates that the cylinder is undercharged and may not provide adequate oxygen for the duration required in an emergency. Lastly, if the pointer is in the red zone, it indicates a critically low charge, rendering the oxygen system unreliable for safety purposes. Therefore, the black band between 1800 - 2500 psi is the optimal range that ensures availability and safety for the emergency oxygen supply during flights.