**Core Concept**
Osteosarcoma is a primary malignant bone tumor characterized by its aggressive growth and production of immature bone matrix. The "sunburst" appearance with bone destruction, soft tissue mass, new bone formation, and sclerosis limited to the metaphysis is a classic radiographic feature of osteosarcoma.

**Why the Correct Answer is Right**
The sunburst appearance is caused by the rapid growth of osteoid tissue, which pushes through the cortex and forms a characteristic radiating pattern of new bone formation. This is accompanied by bone destruction, soft tissue mass, and sclerosis due to the tumor's aggressive nature and its ability to produce osteoid matrix. The metaphyseal location is also typical of osteosarcoma, as it arises from the region where bone growth is most active.

**Why Each Wrong Option is Incorrect**
**Option A:** Osteoma is a benign bone tumor that typically presents as a small, well-defined bony lesion, often with a sclerotic appearance. It is not associated with the aggressive features seen in this case.
**Option B:** Osteoid osteoma is a benign tumor that presents with a characteristic "nidus" or central nidus surrounded by a zone of sclerosis. It is typically smaller and less aggressive than osteosarcoma.
**Option C:** Osteoblastoma is a rare, benign bone tumor that can present with a mixed radiographic appearance, but it is typically smaller and less aggressive than osteosarcoma.

**Clinical Pearl / High-Yield Fact**
Osteosarcoma is the most common primary malignant bone tumor in children and adolescents, and it often presents with pain and a palpable mass. The "sunburst" appearance on radiographs is a classic feature, but a biopsy is necessary to confirm the diagnosis.

**✓ Correct Answer: D. Osteosarcoma**