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.
Answer:
1-46
2-18
Explanation:
c=12 H=1 O=16
ethanol (12×2)+(6×1)+(16)=46
water (2×1)+(16)=18
Atoms are never rearranged
