Which command configures full duplex on an interface?

The command that configures full duplex on an interface is "duplex full." This command is used in the interface configuration mode of Cisco devices to set the duplex mode, allowing the interface to send and receive data simultaneously, which is a feature of full duplex communication.

In networking, full duplex is crucial for optimizing performance, as it allows for more efficient data transmission and minimizes collisions that can occur in half duplex settings. By using this command, network administrators ensure that the interface operates in the most effective mode possible, particularly in environments where bandwidth utilization is critical.

The other choices listed do not conform to the correct syntax for configuring the duplex settings in Cisco IOS. "full duplex," "set duplex full," and "configure duplex full" would not be recognized as valid commands in this context, which is essential for achieving the desired configuration on the network device.