**Core Concept**
Melorheostosis is a rare bone disorder characterized by abnormal bone formation and cortical thickening, often leading to distinctive radiographic features. The condition is also known as "flowing wax" or "melting wax" appearance due to the unique pattern of bone growth.

**Why the Correct Answer is Right**
Melorheostosis is associated with an abnormality in the periosteum, the fibrous layer covering the bone surface. This leads to increased bone formation and cortical thickening, resulting in the characteristic "molten wax" appearance on radiographs. The condition often affects the metaphyseal regions of long bones, where the periosteum is most active.

**Why Each Wrong Option is Incorrect**
**Option A:** Achondroplasia is a genetic disorder affecting bone growth, leading to short stature and characteristic radiographic features such as shortened long bones and a small skull base. However, it does not produce a "molten wax" appearance.

**Option B:** Pseudogout, also known as calcium pyrophosphate deposition disease (CPPD), is a type of crystal-induced arthritis characterized by calcium pyrophosphate dihydrate (CPPD) crystal deposition in joint cartilage and bone. While it can cause calcification and ossification in the joint space, it does not produce a "molten wax" radiographic appearance.

**Option D:** Osteopetrosis is a rare genetic disorder characterized by increased bone density due to impaired osteoclast function. While it can cause a range of radiographic abnormalities, including cortical thickening and sclerosis, it does not produce a "molten wax" appearance.

**Clinical Pearl / High-Yield Fact**
Melorheostosis is often bilateral and can affect multiple bones, but it typically spares the epiphyses and growth plates. Awareness of this distinctive radiographic feature can help in the early diagnosis and management of this condition.

**✓ Correct Answer: C. Melorheostosis**