The empirical formula for a compound is ch2. if  n  is a whole number, which shows a correct relationship between the molecular formula and the empirical formula?  

An empirical formula is the "reduced" version of a molecular formula. For example, CH3 is the empirical formula for C2H6, C3H9, C4H12, and so forth. The difference in subscripts between an empirical formula and molecular formula is given by the constant n. If n is a whole number, this means the numerator is the molecular formula. So the answer is D. subscript of C in molecular formula = n  subscript of C in empirical formula. This can be rewritten as:

n = subscript of C in molecular formula/subscript of C in empirical formula