# Which property of hydrogen fluoride causes it to be a weak acid in an aqueous solution?

$\left(i\right)$ strength of the $H - F$ bond, and $\left(i i\right)$ charge density of the fluoride ion.
$H - X + {H}_{2} O r i g h t \le f t h a r p \infty n s {H}_{3} {O}^{+} + {X}^{-}$
The hydrogen fluoride bond is definitely stronger than the $H - C l$ or $H - B r$ bond; and thus enthalpy disfavours the forward reaction. More importantly, the ${F}^{-}$ ion is smaller and more polarizing than $C {l}^{-}$ or $B {r}^{-}$. ${F}^{-}$ is thus disfavoured by entropy, in that it causes more solvent order.