What nitrogenous base is found exclusively in RNA?

The nitrogenous base that is found exclusively in RNA is uracil. In RNA, uracil takes the place of thymine, which is present in DNA. This distinction is one of the primary differences between the two nucleic acids. While adenine and cytosine are found in both DNA and RNA, uracil is unique to RNA, serving a similar role as thymine does in DNA for pairing with adenine during the formation of RNA molecules. This structural variation contributes to RNA's functions, such as during protein synthesis and gene expression.