Final answer:
The most likely diagnosis for a sunburst appearance on an X-ray is osteosarcoma, which is a type of bone cancer.
Step-by-step explanation:
The most likely diagnosis for a sunburst appearance on an X-ray is osteosarcoma, which is a type of bone cancer. Osteosarcoma often presents as a sunburst pattern on X-rays due to the irregular growth of cancerous cells in the bone, resembling the rays of the sun. This pattern occurs when the tumor breaks through the bone and stimulates abnormal bone growth.