According to Genesis, Noah took one pair of each unclean animal into the Ark.
Genesis 7:2 distinguishes between clean and unclean animals. It instructs Noah to take seven pairs of every clean animal, but only one pair of every animal that was not clean. Genesis 7:8–9 then summarizes animals entering the ark in pairs, male and female.
The “one pair” answer applies specifically to unclean animals. It should not be generalized to every animal in the account, because the clean-animal instruction uses a different number. Genesis does not provide a modern zoological list defining every species included in either category.
Some translations phrase the clean-animal instruction as seven animals or seven pairs, creating a translation discussion. The unclean-animal instruction is consistently presented as two individuals, one male and one female, making one pair the clearest concise answer.