**Core Concept**
Chondrosarcoma is a malignant primary bone tumor arising from cartilage, typically in adults, and is characterized by the formation of cartilaginous tissue with malignant transformation. It is distinct from benign cartilage-forming tumors due to its invasive growth and high risk of metastasis.

**Why the Correct Answer is Right**
Chondrosarcoma is the only malignant bone tumor listed. It originates in cartilage cells and shows atypical mitotic activity, necrosis, and infiltrative growth patterns. It commonly occurs in the pelvis, femur, and humerus, and is classified by grade based on cellular atypia and mitotic rate. Unlike benign tumors such as osteoid osteoma, chondroma, or osteochondroma, chondrosarcoma has a high risk of local recurrence and metastasis, especially in high-grade forms.

**Why Each Wrong Option is Incorrect**
Option A: Osteoid osteoma is a benign, painful bone tumor of young adults, often treated with NSAIDs or surgery, and does not exhibit malignant features.
Option B: Chondroma is a benign tumor of cartilage, usually found in the epiphysis of long bones, with no malignant potential.
Option D: Osteochondroma is a benign, common bone tumor arising from cartilage, typically in adolescence, and grows slowly without malignancy.

**Clinical Pearl / High-Yield Fact**
Remember: "Chondrosarcoma = Malignant, cartilage origin, high-grade, metastatic potential." Benign cartilage tumors (chondroma, osteochondroma) are common but not malignant—only chondrosarcoma is malignant among the options.

✓ Correct Answer: C. Chondrosarcoma