Which command can be used to initiate the Disk Defragmentation process?

The command used to initiate the Disk Defragmentation process is "defrag." This command is specifically designed to reorganize fragmented data on a hard drive to improve the overall performance and efficiency of the system. When you run this command, it analyzes the files on the disk and consolidates fragmented pieces, allowing for faster access and retrieval of data.

The other options serve different purposes. For example, "cleanmgr.exe" is used to launch the Disk Cleanup utility, which helps to remove unnecessary files from the system to free up disk space but does not perform defragmentation. "chkdsk" is a command used to check the file system and file system metadata of a volume for logical and physical errors, but it does not reorganize data. "diskpart" is a powerful command-line utility for managing disks, partitions, and volumes, but it is not related to defragmentation tasks.

Thus, "defrag" is specifically tailored for disk defragmentation, making it the correct choice for initiating that process.