Explanation

I.
II.
III. `H.C. (Mw = 70)`. It should have `C_(5)`
If it is `C_(5) H_(12) Mw = 60 + 12 = 72`
If it is `C_(5) H_(10). Mw = 60 + 10 = 70`.
So it should be `C_(5)H_(10). [It has `1^(@) of unsaturation.
It cannot be alkene
SInce it is an alkane,
so it si cyclic,]
IV.