After applying handbrakes in the proper place, what must be done to verify that they will prevent movement?

Releasing all air brakes after applying the handbrakes is essential for verifying that the handbrakes can effectively prevent movement. When the air brakes are released, it eliminates any air pressure that might otherwise hold the train in position, allowing you to test the efficacy of the handbrakes alone. If the handbrakes are functioning properly, the train should remain stationary without the support of the air brakes. This procedure is critical because it ensures that the handbrakes will act as a reliable measure of safety when the air brakes are not engaged.

Other methods, while important for overall safety checks, do not provide the same verification certainty. Checking the air pressure can give an indication of whether the air braking system is functioning, but it does not directly assess the effectiveness of the handbrakes. Inspecting the safety chain might ensure that additional safety measures are in place, but it is not directly related to the performance of the handbrakes themselves, and visual inspections, while informative, do not demonstrate whether the handbrakes can hold the train in position under load.