HF is the weakest hydrohalic acid in water although the H-F bond is the most polar. The chief reason is

1. AF is less electronegative than Cl
2. Bthe H-F bond dissociation enthalpy ($574\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$) is much higher than that of H-Cl ($431\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$), so ionisation is less favourable
3. CHF cannot form hydrogen bonds with water
4. Dthe F- ion is larger than the Cl- ion