Which of these structures appears radiopaque?: (A) Maxillary sinus, (B) Nasal fossa, (C) Nasal septum, (D) Mental foramen
Answer is C. Radiopaque refers to that portion of the radiograph that appears light or white. Radiopaque structures are dense and absorb or resist the passage of the X-ray beam, E.g., Enamel, dentin and bone.
Nasal septum
On the panoramic radiograph, it appears as a vertical radiopaque partition that divides the nasal cavity.
Reference: Freny R Karjodkar Oral Radiology Principles and Interpretation 2nd  edition page no 251