Final answer:
The correct radiographic position to place the right SI joint perpendicular to the IR is a 25-30 degree RAO projection.
Step-by-step explanation:
The question pertains to the positioning of a patient for a radiographic examination where the right sacroiliac (SI) joint is to be perpendicular to the image receptor (IR). The correct position that would achieve this orientation is b. 25-30 degree right anterior oblique (RAO) projection. In this position, the patient is rotated such that the right SI joint is closest to the image receptor and therefore would be depicted perpendicular on the radiographic image. This is a specific positioning technique used in radiographic imaging to allow clear visualization of anatomical structures. Options a, c, and d do not achieve the correct orientation for a perpendicular view of the right SI joint.