Final answer:
Fructose-6-phosphate and glucose-6-phosphate are best characterized as stereoisomers, which means they have the same chemical formula but differ in the spatial arrangement of their atoms.
Step-by-step explanation:
Fructose-6-phosphate and glucose-6-phosphate are best characterized as stereoisomers. Stereoisomers are compounds that have the same chemical formula but differ in the spatial arrangement of their atoms. In this case, the two compounds have the same chemical formula, but their structures differ due to the different positions of the phosphate group.
They are not epimers because epimers are sugars that differ in the configuration around one specific carbon atom. Fructose-6-phosphate and glucose-6-phosphate have different positions of the phosphate group, not a difference in configuration around a carbon atom.