Final answer:
The A&P technician/inspector must perform an operational check to ensure the aircraft is airworthy after a 100-hour inspection.
Step-by-step explanation:
The specific operational check that must be performed by the A&P technician/inspector prior to returning a complete aircraft to service as airworthy following a 100 hour inspection is known as the 'Operational Check'. This check involves testing the different systems and components of the aircraft to ensure they are functioning correctly. For example, the technician/inspector may check the engine, landing gear, flight controls, electrical systems, and avionics.