Which format involves writing zeros to the whole disk, making data unrecoverable?

The full format option is the correct choice because it includes the process of writing zeros to every sector of the disk, effectively erasing any existing data. This thorough approach means that once a full format is completed, the data that was previously on the disk becomes exceedingly difficult, if not impossible, to recover using standard data recovery methods.

In addition to erasing the data, a full format also checks the disk for bad sectors and can mark them so they won't be used in the future. This serves both to prepare the disk for new data and to ensure its reliability going forward. By contrast, other formatting options may not include this comprehensive data deletion process, focusing instead on simply preparing the file system for new data or making partitions without the data-wiping feature.