Final answer:
The film placement most likely to excite the gag reflex is the posterior periapical.
Step-by-step explanation:
The film placement most likely to excite the gag reflex is the posterior periapical. In dentistry, periapical radiographs are used to examine the entire tooth, including the roots and surrounding bone.
The posterior periapical film placement involves placing the film towards the back of the mouth, causing a gag reflex in some individuals. It is important for the patient to try to relax and breathe through their nose during the procedure to minimize discomfort.