Biologists divide mechanisms of reproductive isolation into

The correct answer will be - prezygotic and postzygotic

Explanation:

Reproductive isolation is the mechanism of speciation which suggests that species gets isolated and do not mate due to reproductive barriers.

These barriers could be the pre-zygotic barriers which represent the barrier before the formation of the zygote that is fertilization of the egg and sperm.

The post-zygotic barrier represents the condition in which the species are isolated due to barriers arisen due to formation of the sterile offsprings.

Thus, pre-zygotic and post-zygotic is the correct answer.