Explanation:
It is known that stronger is the bonding between the atoms of a molecule more difficulty it will face to form vapors. Hence, more heat needs to be provided to the molecule. As a result, it will have high boiling point.
So, in heptanol there is hydrogen bonding. Hence, there is strong bonding so, boiling point of heptanol will be high.
On the other hand, heptane has long carbon chain as compared to pentane. Therefore, heptane will occupy more surface area and thus, more heating will be provided to it. Hence, boiling point of heptane will be greater than the boiling point of pentane.
Thus, we can conclude that rank of given compounds according to start of their boiling point is as follows.
pentane < heptane < heptanol