Final answer:
A teratogenic substance causes fetal malformation, such as limb defects from Thalidomide or developmental disorders from alcohol exposure. The severity of such defects depends on the teratogen's potency, fetal susceptibility, and dosage.
Step-by-step explanation:
A teratogenic substance is an agent that causes malformations of an embryo or fetus. The correct answer to the question presented is (c) causes fetal malformation. Teratogens can be drugs, chemicals, or even environmental factors like radiation and can cause a range of birth defects. An example of a teratogen is Thalidomide, which, due to its enantiomeric structure, caused limb defects when taken by pregnant women in the past. Other common teratogens include alcohol, which can cause fetal alcohol spectrum disorders (FASD), and various prescription and over-the-counter drugs, which can lead to a myriad of developmental problems. When exposure to a teratogen occurs, the level of harm it can cause depends on factors such as potency, fetal susceptibility, and dosage.