Hexane and 2-methylpentane. If you draw the structures out, you can see that both isomers have 6 carbon atoms and 14 hydrogen atoms. Hence they have the same molecular formula but a different structural formula. I suggest drawing the compounds out for these types of questions to visualise it.
All elements are made up of atoms. ➢ Atoms are made up of protons, neutrons, and electrons. Two different kinds of atoms can combine to form a compound. A molecule is a combination of atoms that cannot be broken apart while still retaining the same properties as the larger substance that it is a part of.