Which of the following is an example of a teratogen?

A teratogen is an environmental agent that can cause developmental malformations in a fetus or embryo when exposure occurs during critical periods of development. Smoking is classified as a teratogen because it contains harmful substances, such as nicotine and carbon monoxide, which can negatively affect fetal development. Research has shown that maternal smoking during pregnancy can lead to low birth weight, preterm birth, and increased risk of developmental issues.

In contrast, folic acid and vitamin C are actually beneficial nutrients that support healthy development during pregnancy. Folic acid is known to help prevent neural tube defects in the developing fetus, while vitamin C is important for tissue repair and overall health. Sodium, although essential in moderation for bodily functions, does not fall into the category of teratogens; however, excessive sodium intake can lead to health issues such as hypertension in mothers but does not directly cause malformations in the fetus. Therefore, smoking is the clear example of a teratogen in this context.