The correct option is B 3>1>2
The boiling point of organic compounds depends on two factors:
i) Molecular weight: boiling point increases with increase in molecular weight.
ii) Intermolecular forces: higher the strengh of intermolecular forces, higher is the boiling point.
Butanoic acid forms extensive intermolecular hydrogen bonding than butanol. Carboxylic acids have the ability of forming a dimer by hydrogen bonding that leads to a stable arrangement. Hence, they have higher boiling points.
Butanal has a lower boiling point than the two due to comparitively weaker dipole-dipole interactions.