Nucleotide is structural and functional unit of nucleic acids. Each nucleotide is has sugar molecule (ribose or deoxyribose), phosphate moiety and nitrogenous base. There are two types of nitrogenous bases, namely purines (adenine and guanine) and pyrimidines (thymine, uracil and cytosine). The base of a nucleotide is joined covalently (at N-1 of pyrimidines and N-9 of purines) in an N –beta- glycosyl bond to the 1’ carbon of sugar. The phosphate is esterified to the 5’ carbon. This makes options A and D incorrect as a nucleotide can have either purine or pyrimidine. Option B is incorrect as sugar molecule is component of nucleotides.