A compound has the empirical formula CH2O and a relative molecular mass of 180. Its molecular formula is

Explanation

The empirical formula mass is 12 + 2 + 16, that is 30, and 180 divided by 30 gives 6, so every subscript is multiplied by six to give C6H12O6, which is glucose. The empirical formula gives only the simplest whole number ratio of atoms, while the molecular formula gives the actual number in one molecule. The two coincide only when that multiplier happens to be one.