* They always show the exact arrangement of atoms within a molecule. Chemical formulas only show the types and quantities of atoms, not their 3D structure. For example, both glucose and fructose have the same chemical formula (C6H12O6), but they have different structures.
* They always represent a single molecule. Chemical formulas can represent a single molecule, but they can also represent a repeating unit in a larger structure like a polymer or a formula unit in an ionic compound.
* They always include all the elements present in a substance. While the main elements are always represented, trace amounts of impurities or elements that are not essential to the substance's identity might not be included in the chemical formula.
Therefore, the most accurate answer to your question is:
Chemical formulas do not always show the exact arrangement of atoms within a molecule.
