**Core Concept**
Thrombocytopenia, macerated skin lesions, rash, and periostitis in a newborn are classic manifestations of congenital syphilis, a condition resulting from the transplacental transmission of *Treponema pallidum* from the mother to the fetus.

**Why the Correct Answer is Right**
Congenital syphilis occurs when the mother has active syphilis infection during pregnancy, leading to the transmission of the causative agent, *Treponema pallidum*. This results in various systemic manifestations, including thrombocytopenia due to bone marrow suppression, macerated skin lesions (also known as "snuffles"), rash, and periostitis, which is inflammation of the periosteum, a layer covering the bones. The presence of these symptoms in a newborn suggests congenital syphilis.

**Why Each Wrong Option is Incorrect**
**Option A:** Erythroblastosis fetalis is a condition characterized by the presence of antibodies against the RhD antigen in the mother's blood, leading to hemolysis of the fetus's red blood cells. While it is a serious condition, it does not cause thrombocytopenia, macerated skin lesions, rash, and periostitis in the newborn.

**Option B:** Cytomegalovirus (CMV) infection is a common cause of congenital infection, leading to symptoms such as microcephaly, vision and hearing loss, and developmental delays. However, it does not typically cause the specific combination of symptoms seen in congenital syphilis.

**Option D:** HIV infection can be transmitted from mother to child during pregnancy, childbirth, or breastfeeding, but it does not cause the specific combination of symptoms seen in congenital syphilis.

**Clinical Pearl / High-Yield Fact**
Congenital syphilis is a preventable condition, and prompt diagnosis and treatment of the mother's syphilis infection during pregnancy can prevent transmission to the fetus. A high index of suspicion for congenital syphilis is essential in newborns presenting with these symptoms.

**✓ Correct Answer: C. Syphilis**