Which of the following is the simplest unit of a nucleic acid

Nucleotides are made of a pentode sugar, a phosphate and a nitrogen base. Nucleotides are the building blocks of nucleic acids DNA and RNA which serve as the cell's store house of genetic information. All nucleotides are composed of three parts: a five-carbon sugar, a phosphate and a nitrogen-rich structure called a nitrogenous base. The sugar can be ribose which is found in RNA, or deoxyribose which is found in DNA. The only difference between these two sugars is that deoxyribose has one fewer oxygen atom than ribose.

1.fossils 2.analogous organs 3.homologous organs