Nucleotide are building blocks of nucleic acids, nucleotide is a composite molecule formed by:

A nucleotide is a composite molecule formed by a base, a sugar, and a phosphate group. The base is a nitrogenous base, the sugar is a five-carbon sugar, and the phosphate group is a phosphate molecule. So, the correct answer is option C. Notice that the other options are not correct. Option A is a representation of a nucleic acid, which is a polymer of nucleotides. Option B is a representation of a nucleoside, which is a base linked to a sugar. Option D is a representation of a sugar-phosphate molecule, but it is not a complete nucleotide.