Which of the following
parts of the diagram represents the portion of dna composed
of the nucleotides' phosphate groups?

a. x
b. both w and x
c. w
d. y

Phosphate groups of the nucleotides in the diagram are marked with W.

Option C.

DNA is a macro molecule which is formed of polymerization of deoxyribonucleotides. Four types of deoxyribonucleotides are present which are adenosine, guanosine, thymidine and cytosine triphosphate. These nucleotides are polymerized based on the genetic setup.

The phosphate groups attached with the sugar molecule are actually polymerized with the o glycosidic bond. That's marked with the letter W. These phosphate molecules are attached with the sugar molecules which actually are attached with the nitrogen bases. They in total forms a nucleotide, hence the whole DNA. X in the diagram are nitrogen bases and the Y are the hydrogen bonds between the complementary nitrogen bases