According to Genesis, Noah took seven pairs of clean animals onto the Ark.
Genesis 7:2 instructs Noah to take seven pairs—traditionally understood as seven male-and-female pairs—of every clean animal, while taking one pair of each unclean animal. Genesis 7:3 separately mentions seven pairs of birds, and Genesis 7:8 distinguishes clean animals, unclean animals, birds, and creatures that move on the ground.
A common simplified retelling says that Noah took two of every animal. That captures the basic preservation idea, but Genesis adds a distinction between clean and unclean animals. The reason is connected to later sacrifice: after leaving the ark, Noah builds an altar and offers some clean animals and birds in Genesis 8:20.
The passage does not provide a modern zoological list or explain every classification in contemporary biological terms. “Clean” and “unclean” are ritual categories in the biblical narrative. The precise answer is therefore the category named in Genesis, not a particular species such as sheep or cattle.