In Genesis, one pair of animals described as unclean entered Noah’s Ark.
Genesis 6:19–20 gives the broad instruction that Noah should bring a male and female of every kind of living creature. Genesis 7 then adds a distinction: seven pairs of clean animals and birds, but one pair of animals that are not clean. This is why the story can contain both the familiar “two of every kind” idea and a larger number for clean animals.
The passage does not provide a complete species-by-species list of which creatures were clean or unclean. The categories are related to later biblical dietary classifications, but Genesis does not spell out the full system at this point in the narrative.
Many children’s summaries say simply that two of every animal entered the Ark. That is a useful simplification of the general instruction, but the detailed Genesis passage distinguishes clean from unclean animals. For the unclean category, the stated number is one pair.