Two "naked" (without histones or other proteins) double-stranded fragments of dna are exactly the same length. at 89°c, fragment a has completely denatured, which means that the two strands have separated. at that temperature, fragment b is still double-stranded. how might these fragments differ, to result in different denaturation temperatures?

Fragment B has a higher C/G base pair content.

Explanation:

DNA denaturalization happens when the double helix melts and the result is two single strands. The separation occurs because the hydrogen bonds between the bases, break apart.

DNA denaturalization occurs faster in the regions where the interaction between the two strands is weak, A/T rich regions. On the other hand in C/G rich regions, the strand is held together more strongly hence, it takes more time for it to break apart.

DNA with a lot of A/T base pairs denatures at 158 °F  (70°C) and DNA rich with C/G base pairs denatures at over 212 °F (100°C). C≡G base pairs have three hydrogen bonds, the bond is very stable and needs a lot of energy to be dissociated. The higher the C≡G base pairs content, the higher the melting point of the DNA.