Which statement distinguishes empirical and molecular formulas?

• A. The empirical formula shows the simplest ratio of atoms; the molecular formula shows the exact numbers in a molecule
• B. The empirical formula shows the exact numbers; the molecular formula shows the smallest ratio
• C. They are always identical
• D. The empirical formula shows charge balance

Answer: (A)

The key idea is that empirical and molecular formulas convey different levels of detail about a compound’s composition. The empirical formula is the simplest whole‑number ratio of the atoms present in the substance, which you find from data like percent composition by converting to moles and reducing to the smallest integers. The molecular formula shows the actual number of each type of atom in a single molecule, which can be the same as the empirical formula or a whole‑number multiple of it, determined by the compound’s molar mass.

This distinction is why the statement about the empirical formula showing the exact numbers isn’t correct—the molecular formula does that. It’s also why the molecular formula isn’t necessarily the smallest ratio—the empirical formula is. And empirical formulas aren’t about charge balance; they’re about the simplest atom counts. An example is glucose, whose empirical formula is CH2O, while its molecular formula is C6H12O6, six times the empirical.