The boiling point is related to the energy required for the molecules of a compound to go from a liquid state to a gaseous state. The higher the energy required, the higher the boiling point.
Now, this energy will depend on the number of bonds in the molecule and their bond types. The longer the molecule, the more bonds it will have and the more energy it will need. Also, a double bond will require more energy than a single bond.
Let's see then the types of molecules we have. We have 4 molecules that correspond to organic acids, all these acids have single bonds, so on that side, the boiling points would be similar. What changes is the length of the chain that accompanies the carboxylic group (COOH).
Let's count the number of atoms of each element in the molecules:
In the table we see the number of moles, the higher the number of carbon atoms, the longer the chain will be and the boiling point will be higher. The hydrogen atoms will depend on the carbon atoms since they are attached to them, so we can simply rely on the number of carbon atoms to order the compounds.
Therefore, the order of the acids from the highest boiling point to the lowest boiling point will be:
1.Octadecanoic acid
2.Octanoic acid
3.Butanoic acid
4.Methanoic acid