What should be done if defective air brake devices are discovered and brakes do not release?

Answer: B — Stop the train as soon as possible

Stopping the train as soon as possible is the appropriate action when defective air brake devices are discovered, and the brakes do not release. This is crucial because malfunctioning brakes can lead to a potential safety hazard on the railroad. If a train cannot stop properly, it poses risks not only to the train crew and its passengers but also to anyone else in the vicinity, including vehicles and personnel near the tracks. By stopping the train promptly, the crew can assess the situation, implement emergency procedures, and ensure that it does not result in an accident. This action prioritizes safety and allows for the proper evaluation of the brake issues before any further actions are taken, such as notifying maintenance personnel or conducting a thorough inspection of the brake system. Other options, while they may seem relevant, do not address the immediate safety risk associated with defective brakes. Escalating train speed could exacerbate the situation, and inspecting all passenger cars or merely notifying a crew leader would not provide a timely solution to the malfunctioning brakes issue. The priority in such a scenario is to ensure the train is secured and under control to prevent any potential incidents.