Final answer:
If a sending system does not know the MAC address of the intended recipient system, it sends a broadcast frame with the MAC address FF-FF-FF-FF-FF-FF.
Step-by-step explanation:
If a sending system does not know the MAC address of the intended recipient system, it sends a broadcast frame with the MAC address FF-FF-FF-FF-FF-FF. This MAC address is a special value that represents a broadcast to all systems on the local network. By using this address, the sending system can reach out to all systems and request the MAC address of the intended recipient.