Final answer:
Pilots using VFR must monitor the mandatory frequency until they are beyond the MF area or have landed, to ensure safety by being aware of other aircraft.
Step-by-step explanation:
If a mandatory frequency (MF) is in use, the pilot departing VFR (Visual Flight Rules) shall monitor that frequency until the aircraft is beyond the MF area or has landed. The purpose of an MF is to ensure that all aircraft in the area are aware of each other's presence and intentions, thereby reducing the risk of a collision. It's important for pilots to pay attention to such requirements to maintain safety in aviation.