**Core Concept**
The question requires identification of radiopacities on a radiograph, specifically in the mandible. The correct answer involves recognizing anatomical structures that produce symmetrical radiopacities.

**Why the Correct Answer is Right**
Mental ridges are bony projections on the anterior aspect of the mandible, one located on each side of the midline. They are formed by the fusion of the mental spines of the mandible and the alveolar bone. These ridges are visible on radiographs due to the presence of dense bone and are often used as landmarks for dental and orthognathic procedures. The mental ridges are symmetrical, meaning they appear on both sides of the mandible, which is consistent with the description provided in the question.

**Why Each Wrong Option is Incorrect**
* **Option A:** The genial tubercle is a small bony projection located on the anterior aspect of the mandible, but it is not symmetrical and is not typically visible on radiographs as a distinct radiopacity. It is located on the anterior aspect of the mandible and serves as an attachment point for the genioglossus muscle.
* **Option C:** Mylohyoid ridges are bony projections located on the inner surface of the mandible, but they are not typically visible on radiographs as symmetrical radiopacities. They are more relevant to the attachment of the mylohyoid muscle and are not commonly used as landmarks for dental or orthognathic procedures.

**Clinical Pearl / High-Yield Fact**
When interpreting radiographs of the mandible, it is essential to recognize the presence of mental ridges as a normal anatomical variant. These ridges can be mistaken for pathologic processes, such as tumors or cysts, if not recognized correctly.

**✓ Correct Answer: B. Mental ridges**