Which information must be known about a compound to find the molecular formula from the empirical formula

Molecular mass or vapor density

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.

the answer is c a tornado