What is one part of a nucleotide that differs among the four different nucleotides?

The part of a nucleotide that differs among the four different nucleotides is the nitrogenous base.

Explanation:

Nucleic acids such as DNA and RNA are made up of monomers called nucleotides. A nucleotide contains a phosphate group, a five-carbon sugar (ribose or deoxyribose), and a nitrogenous base (nucleobase). The nucleotide in DNA contains a phosphate group attached to a five-carbon deoxyribose sugar molecule and one of the four nitrogenous bases: adenine, guanine, cytosine or thymine. The nucleotide in RNA contains a phosphate group attached to a five-carbon ribose sugar molecule and one of the four nitrogenous bases: adenine, guanine, cytosine or uracil.

not sure if this what   you'r looking for would be percent composition