Final answer:
The projection of the thumb that requires digits two through five to be extended, with the palmar surface of the hand flat against the IR as if for a PA hand projection, is supination of the forearm.
Step-by-step explanation:
The projection of the thumb that requires digits two through five to be extended, with the palmar surface of the hand flat against the IR as if for a PA hand projection, is the a. hand from the palm backward position to the palm forward position. This movement is also known as supination of the forearm.