Which of the following is a unique address assigned to hardware devices such as modems and network interface cards?

A MAC address is a unique identifier assigned to hardware devices, such as modems, network interface cards, and other networked hardware. This address is essential for network communication within a local area network (LAN) because it enables the identification and differentiation of devices on the network.

The MAC address is a physical address that operates at the data link layer of the OSI model, allowing devices to communicate with each other on the same physical network segment. It is typically presented in hexadecimal format and is hardcoded into the hardware during manufacturing.

Understanding the roles of other addresses helps clarify why the MAC address is the correct answer. An IP address, while it is also unique, serves a different purpose on broader networks such as the Internet. It works at the network layer and can change depending on the device's connection to different networks. Similarly, a DNS address is associated with domain name resolution rather than hardware identification, while a gateway address refers to the device that acts as an access point for forwarding traffic between different networks. Each of these serves a distinct function within network communications, reinforcing the uniqueness and significance of the MAC address for hardware identification.