**Core Concept**
Vertical transmission refers to the passage of a pathogen or disease from mother to offspring during pregnancy, childbirth, or breastfeeding. This mode of transmission is a significant public health concern, as it can lead to severe consequences, including congenital infections, birth defects, and neonatal mortality.

**Why the Correct Answer is Right**
The correct answer is related to the fact that vertical transmission often involves the transfer of pathogens through the placenta, fetal membranes, or breast milk. For example, human immunodeficiency virus (HIV) can be transmitted from mother to child during pregnancy, childbirth, or breastfeeding. Similarly, hepatitis B virus (HBV) can be transmitted vertically through the placenta or during birth.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because vertical transmission is not typically associated with airborne pathogens, which are usually spread through respiratory droplets or contact with contaminated surfaces.
**Option B:** This option is incorrect because horizontal transmission refers to the spread of a pathogen from person to person through direct or indirect contact, rather than from mother to child.
**Option C:** This option is incorrect because congenital syphilis is a classic example of vertical transmission, but it is not the only correct answer.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that vertical transmission can occur with various pathogens, including viruses, bacteria, and parasites. Healthcare providers must take a thorough history and perform appropriate screening tests to identify pregnant women at risk of vertical transmission.

**Correct Answer: C. Congenital syphilis.**