Which of the following compounds is most soluble in water?

Propanoic acid and either version of propanol are liquids which are all completely miscible with water, which means that the liquids combine in any proportion, which of course means that they are quite soluble in water. This is ociated with the hydrogen bonding between these compounds and water. You would have to say that (a) and (d) are equally good answers. The solubilities of 1-bromopropane and propane are a distant third and fourth, respectively.