RNA (Ribonucleic Acid) differs from DNA in its nucleotide makeup. The nitrogenous bases in RNA are: Adenine (A), Guanine (G), Cytosine (C), and Uracil (U).
Thymine (T) is absent in RNA. Uracil (U) replaces it and pairs with Adenine during transcription.
Key Points: Thymine is exclusive to DNA. Uracil is specific to RNA and is chemically similar to Thymine but lacks a methyl group. Consequently, the correct identification is Thymine.