Carboxylic acids with even number carbon atoms have higher melting point than
those with odd number carbons atom. Among acetic acid and butanoic acid the latter
molecules face more repulsion hence acetic acid has higher melting point
Here, acetic acid CH3COOH has the highest boiling point among the given compound. This is because it forms a dimer with the help of intermolecular hydrogen bonding.
Because of intermolecular hydrogen bonding, it has the highest boiling point.