Which of the following is an example of a teratogen?

A teratogen is an agent or factor that causes malformation or abnormal development of an embryo or fetus, leading to birth defects. Alcohol is categorized as a teratogen because its consumption during pregnancy can lead to a range of physical, behavioral, and cognitive issues in children, collectively known as Fetal Alcohol Spectrum Disorders (FASD). These disorders can result from the fetus being exposed to alcohol, which can interfere with normal development processes.

In contrast, the other options—Vitamin C, Calcium, and Iron—are essential nutrients that play crucial roles in the healthy development of a fetus. While excessive or inadequate amounts of certain nutrients can lead to complications, they are not classified as teratogens. Instead, they contribute positively to the well-being and healthy growth of both the mother and the developing fetus. Thus, alcohol's adverse effects on fetal development clearly align with the definition of a teratogen, making it the correct answer.