Final answer:
In ICD-10-PCS, the correct root operation for removing a thumbnail is 'Extraction'. This option is chosen because it matches with the description of pulling out a portion of a body part, which accurately characterizes the removal of a thumbnail.
Step-by-step explanation:
In the ICD-10-PCS (International Classification of Diseases, 10th Revision, Procedure Coding System), the correct root operation for coding the removal of a thumbnail would be extraction. The root operation extractions refers to pulling or stripping out or off all or a portion of a body part by the use of force. The other options, such as extirpation, which involves taking or cutting out solid matter from a body part, removal, which refers to taking out or off a device from a body part, and fragmentation, which denotes breaking solid matter in a body part into pieces, do not appropriately describe the procedure of removing a thumbnail.