The best method for the separation of naphthalene and benzoic acid...

Naphthalene can sublime directly to vapour upon heating, but benzoic acid do not. Related Theory When benzoic acid is heated in presence of $a$ strong dehydrating agent like $\mathrm{P}_2 \mathrm{O}_5$ or $\mathrm{H}_2 \mathrm{SO}_f$ it forms benzoic anhydride. 2 \mathrm{C}}_{6} \mathrm{H}}_{5} \mathrm{COOH} \underset{\mathrm{BaOl}_5}{\longrightarrow}\left(\mathrm{C}}_{6} \mathrm{H}}_{5} \mathrm{CO}\right)_2 \mathrm{O}+\mathrm{H}}_{2} \mathrm{O} Caution Naphthalene is volatile and benzoic acid is non-volatile due to the formation of dimer via hydrogen bonding (intermolecular).