**Core Concept**
The **Mongolian spot** is a type of congenital melanocytic nevus, a benign flat blue-grey skin marking. It is commonly found in infants, particularly those of East Asian, Native American, African, and Latino descent.

**Why the Correct Answer is Right**
The most common site for **Mongolian spots** is the **lumbosacral area**, which is the lower back. This is due to the embryological development of the skin and the migration of melanocytes during fetal development. The **lumbosacral area** is a typical location for these spots to appear.

**Why Each Wrong Option is Incorrect**
**Option A:** The face is not a typical location for **Mongolian spots**.
**Option B:** The neck is also an unusual site for these spots.
**Option D:** The leg is not a common location, and **Option E:** the thigh is also not typically involved.

**Clinical Pearl / High-Yield Fact**
**Mongolian spots** usually fade by the age of 5, but it's essential to distinguish them from other skin lesions.

**Correct Answer:** C. Lumbosacral area