Which item from the pushback checklist procedure is responsible for turning on the FDR?

The item from the pushback checklist procedure responsible for turning on the Flight Data Recorder (FDR) is the beacon. The beacon is an important component of the aircraft's safety systems, as it signals to ground personnel and others that the aircraft is powered and preparing for movement. Activating the beacon typically coincides with other systems being initialized, which includes the FDR. This ensures that all relevant data regarding the flight is captured from the moment the aircraft begins its pushback from the gate.

The other items listed serve different purposes. Emergency lights are activated for safety in case of an emergency and do not directly interact with the FDR. Strobes can enhance visibility but are not specifically tied to the operation of the flight recorder. The ground power unit provides electrical power to the aircraft but does not activate the FDR. Thus, the role of the beacon in the pushback checklist specifically includes the activation of critical systems like the FDR, making it the correct choice in this context.