Explanation:
Osteosarcoma is the most common primary malignant bone tumor in adolescents. It typically arises in the metaphysis around the knee and shows aggressive periosteal reactions such as sunburst appearance and Codman triangle. Ewing sarcoma is diaphyseal, chondrosarcoma occurs in older adults, and osteoid osteoma is benign. References: Campbell’s Operative Orthopaedics; WHO Classification of Bone Tumors.