Answer:
Molecular mass or vapor density
Step-by-step explanation:
The empirical formula is the simplest formula of a compound. The molecular formula expresses the exact formula of the compound. To derive the molecular formula, we need information about its molecular mass or if given the vapor density.
(Empirical Formula)n = Molecular formula ------(i)
n = number of repeating units of the empirical formula present in one mole of the molecule
also, (molar mass of empirical formula)n = molar mass of compound
From here, we can find n and insert in (i) above.