Which is the nitrogenous base present only in RNA, but not in DNA?

The nitrogenous base that is present only in RNA and not in DNA is uracil.

Explanation:
Nucleotides: Both RNA (ribonucleic acid) and DNA (deoxyribonucleic acid) are made up of nucleotides, which are the basic building blocks. Each nucleotide consists of a sugar, a phosphate group, and a nitrogenous base.

Nitrogenous Bases: The nitrogenous bases are classified into two categories:

Purines: Adenine (A) and Guanine (G)
Pyrimidines: Cytosine (C) and Thymine (T) (in DNA) or Uracil (U) (in RNA)
Differences Between RNA and DNA:

In DNA: The four nitrogenous bases are adenine (A), thymine (T), cytosine (C), and guanine (G).
In RNA: The four nitrogenous bases are adenine (A), uracil (U), cytosine (C), and guanine (G).
Role of Uracil: Uracil takes the place of thymine in RNA. During the process of transcription, when DNA is converted into RNA, uracil pairs with adenine.

In summary, uracil is unique to RNA, while DNA contains thymine instead.