Empirical formula of a compound is the formula represented by the least ratio of number of atoms of different constituent elements present in the molecule or the formula unit of the compound.
The molecular formula of benzene is
The least ratio of number of atoms of constituent elements being
If no common factor other than 1 is present among the number of atoms of constituent elements in the formula unit of a compound ,then formula unit itself is its empirical formula .
This actually happens in case of Magnesium sulphate having formula unit
So empirical formula of Magnesium sulphate is also