What property of ARP forces all Ethernet NICs to process an ARP request?

The property of ARP (Address Resolution Protocol) that forces all Ethernet NICs to process an ARP request is:

“The destination MAC address FF-FF-FF-FF-FF-FF appears in the header of the Ethernet frame.”
When an ARP request is sent, it is broadcast with a destination MAC address of FF-FF-FF-FF-FF-FF, which is a broadcast address. This means that the frame will be received and processed by all NICs on the local network segment, forcing each NIC to check whether the ARP request is relevant to it. NICs compare the target IP address in the ARP request to their own IP address, and the one that matches responds with an ARP reply. This is how ARP works to resolve IP addresses to MAC addresses on a local network.