Which of the following is NOT a characteristic of isomers?

The statement that isomers share the same structural arrangement is not accurate, which is why it is the correct choice for the question. Isomers are defined as compounds that share the same molecular formula—meaning they contain the same number of each type of atom—but differ in the way those atoms are arranged. This includes differences in structure (structural isomers) or the spatial arrangement of atoms (stereoisomers).

The other characteristics mentioned are true for isomers. They indeed have different chemical properties due to their distinct structural arrangements. Isomers also can exist in multiple forms, which aligns with their nature of presenting different configurations while sharing the same molecular formula. Thus, the correct identification of the statement about sharing the same structural arrangement highlights an essential distinction between isomers and reinforces the concept that structural differences are fundamental to the definition of isomerism.