Question

what do we call a reproductive barrier that allows two species to mate but not produce viable, fertile offspring? prezygotic barrier postzygotic barrier

Explanation:

A postzygotic barrier occurs after fertilization. It prevents the formation of viable, fertile offspring even if mating takes place. A prezygotic barrier prevents mating or fertilization from occurring in the first place. Since the question states that two species can mate but not produce viable, fertile offspring, this is a postzygotic barrier.

Answer:

postzygotic barrier