Answer : Option D) Same empirical formula.
Explanation : In the given molecules of [tex] C_{2} H_{4} [/tex] and [tex] C_{4} H_{8}[/tex] the ratio of C : H atoms in the molecule remains the same i.e 1 : 2.
It means they are in same proportions in both the molecules. Hence, it can be called as the molecules with the same empirical formula. Where empirical formula means the proportions of the elements present in a particular compound are same but differ in arrangement of atoms.