Which of the following nitrogen bases is NOT found in DNA?

Uracil is the nitrogen base that is not found in DNA; instead, it is a key component of RNA. In DNA, the nitrogen bases comprise adenine, thymine, cytosine, and guanine. Adenine pairs with thymine, and cytosine pairs with guanine in the DNA double helix structure. This pairing is essential for the accurate replication of genetic information.

In the case of RNA, uracil replaces thymine and pairs with adenine during the transcription process, where the DNA sequence is copied into RNA. Thus, while adenine, thymine, and cytosine are all integral to the structure and function of DNA, uracil's presence is specific to RNA, making it the correct answer in distinguishing the nitrogen bases exclusive to DNA.