Which component is NOT found in RNA?

The correct answer identifies thymine as a component that is not found in RNA. In RNA, the bases include adenine, uracil, cytosine, and guanine, with uracil specifically substituting for thymine, which is present in DNA. This distinction is crucial to understanding the structural differences between DNA and RNA.

Ribose sugar is indeed a component of RNA, serving as the backbone that connects the nucleotide bases. The phosphate group is also found in RNA, as it forms part of the nucleotides that create the polymerized chain of RNA. Therefore, thymine is unique to DNA, making its absence in RNA a key feature that highlights the differences between these two vital nucleic acids.