The strength of H-bonding depends upon the magnitude of the polarity of the bond. Since H–F bond has maximum polarity (F is the most electronegative element) hydrogen bonding is maximum in HF molecules. - - - $\overset{\delta+}{\mathrm{H}}$ - $\overset{\delta-}{\mathrm{F}}$ - - - $\overset{\delta+}{\mathrm{H}}$ - $\overset{\delta-}{\mathrm{F}}$ --- $\overset{\delta+}{\mathrm{H}}$ - $\overset{\delta-}{\mathrm{F}}$