Which layer of the Open Systems Interconnection reference model (OSI/RM) processes a device's physical address?

The Data Link Layer is responsible for processing a device's physical address, commonly known as the MAC (Media Access Control) address. This layer plays a crucial role in facilitating communication between devices on the same local network. It provides error detection and correction, as well as the framing of data packets for transmission over the physical medium.

In the context of the OSI model, the Data Link Layer sits above the Physical Layer and below the Network Layer. Its primary function is to ensure that data is transferred between devices on the same local area network (LAN) and that the physical addresses of these devices are recognized and utilized effectively during the communication process.

The Transport Layer is mainly concerned with end-to-end communication between devices, managing data flow control, and ensuring complete data transfer. The Application Layer interacts directly with end-user applications and services, dealing with high-level protocols. The Network Layer handles logical addressing and routing of packets across different networks but does not directly deal with physical addresses.

Thus, the Data Link Layer's specific role in managing physical addresses makes it the correct answer.