Final answer:
The unpaired facial bone among the options given is the vomer, which forms the posterior-inferior part of the nasal septum and is solitary, unlike the paired palatine, zygomatic, and lacrimal bones.
Step-by-step explanation:
The facial bones of the skull consist of 14 bones; among these, there are six paired bones and two unpaired bones. The paired bones are the maxilla, palatine, zygomatic, nasal, lacrimal, and inferior nasal conchae bones. The unpaired bones, which only have one of each in the skull, are the
vomer and mandible bones. The vomer bone is especially notable because it is a triangular-shaped bone that forms the posterior-inferior part of the nasal septum, and you can see its whole height when viewed from behind into the posterior openings of the nasal cavity. Therefore, when identifying an unpaired facial bone in the given options (A) palatine, (B) zygomatic, (C) lacrimal, and (D) vomer, the answer is (D) vomer, as it is the only bone in the options that is not paired.