The melting point of carboxylic acid has no trend as we can observe from the following data of metling point.
Methanoic acid =8∘C, Ethanoic acid =17∘C, Propanoic acid =2∘C, Butanoic acid =−6∘C, Pentonoic acid =−35∘C, Hexonic acid =−20∘C, Heptanoic acid =−8∘C, Octanoic acid =17∘C acid. Water solubility of carboxylic acid decreases as we increase the molar mass & hence hydrophobic part of the chain.