**Core Concept**
The most common malignant neoplasm of infancy refers to the most prevalent type of cancer found in infants, which can have distinct characteristics and treatment approaches compared to cancers in older children and adults.

**Why the Correct Answer is Right**
The correct answer is Neuroblastoma, which is a type of cancer that arises from immature nerve cells, or neuroblasts. Neuroblastoma is known to originate in the adrenal glands, but it can also occur in the neck, chest, or pelvis. The high incidence of Neuroblastoma in infancy is due to the fact that it often develops in the first few months of life. The exact cause of Neuroblastoma is still unknown, but it is believed to result from a combination of genetic mutations and environmental factors.

**Why Each Wrong Option is Incorrect**
* **Option A:** Although Langerhans cell histiocytosis can occur in infancy, it is not typically classified as a malignant neoplasm in this age group.
* **Option B:** Medulloblastoma is a type of brain tumor, but it is more commonly found in children aged 3-7 years.
* **Option C:** Rhabdomyosarcoma is a type of soft tissue sarcoma, but it is less common in infancy compared to Neuroblastoma.

**Clinical Pearl / High-Yield Fact**
Neuroblastoma is known for its rapid growth and potential for spontaneous regression in some cases, making it a challenging cancer to treat. Recognizing the distinctive features of Neuroblastoma, such as its high incidence in infancy and its tendency to present with metastatic disease, is crucial for early diagnosis and effective management.

**Correct Answer: C. Neuroblastoma**