Which of the following protocols operates on port 23, allowing remote access to a computer?

Port 23 is designated for the Telnet protocol, which is widely used for remote access to computers. Telnet enables users to log into remote systems over a network as if they were directly connected to those systems. It allows text-based communication with the remote host, and while it was historically significant for managing devices and servers, it does not provide encryption, making it less secure compared to more modern alternatives like SSH (Secure Shell).

The other options relate to different functionalities: FTP, for example, operates on ports 20 and 21 for transferring files, IMAP deals with email retrieval primarily on port 143, and DHCP serves to assign IP addresses dynamically in a network environment, typically using ports 67 and 68. Each of these alternatives serves a distinct role, underscoring that Telnet is uniquely associated with remote access over port 23.