Final answer:
The correct VFR transponder code for flying at or below 12,500 feet is 1200. This code is used to indicate a standard VFR flight not under air traffic control service. Other codes like 7500 and 7700 are for hijacking and emergencies, respectively.
Step-by-step explanation:
The VFR (Visual Flight Rules) transponder code for flying at or below 12,500 feet in the United States is 1200. When flying under VFR, pilots set their transponder to squawk 1200 to signal that they are flying without an individual ATC-assigned code while not under air traffic control service. The other codes provided as options are 7500 for hijacking, 7700 for general emergencies, and 2200 is not a standard transponder code used for VFR flights.