**Core Concept**
The question is testing the identification of a radio-opaque mass associated with the cementoenamel junction (CEJ) of a tooth. The CEJ is the boundary between the enamel of the tooth crown and the cementum of the tooth root. This region is often visible on radiographs due to the presence of a radio-opaque line.

**Why the Correct Answer is Right**
The radio-opaque mass continuous with the CEJ attached to the distal surface of the first premolar is likely a **radiographic sign of a periapical cyst**. A periapical cyst is a type of odontogenic cyst that forms in the periapical region of a tooth, often as a result of pulp necrosis. The cyst may be filled with fluid and can cause resorption of the surrounding bone, leading to a radio-opaque appearance on radiographs. The attachment to the CEJ suggests that the cyst is associated with the root of the first premolar.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not provided, but it could potentially refer to a periapical granuloma, which is a collection of inflammatory cells and granulation tissue that forms in response to pulp necrosis. However, a periapical granuloma would not typically be radio-opaque.
* **Option B:** This option is not provided, but it could potentially refer to a radicular cyst, which is a type of periapical cyst that forms in response to pulp necrosis. However, the term "radicular cyst" is often used to refer to a periapical cyst in general, so this option would be a correct but less specific answer.
* **Option C:** This option is not provided, but it could potentially refer to a calcified pulpaloma, which is a rare condition in which a calcified mass forms in the pulp chamber of a tooth. However, a calcified pulpaloma would not typically be radio-opaque in the same way as a periapical cyst.

**Clinical Pearl / High-Yield Fact**
When evaluating radiographs of the jaw, it's essential to note the presence of a radio-opaque line at the CEJ, as this can indicate the presence of a periapical cyst or other pathology.

**Correct Answer:** B. Periapical cyst.