If a compound AB dissociates to the extent of $75 \%$ in an aqueous solution, the molality of the solution which shows a 2.5 K rise in the boiling point of the solution is $\_\_\_\_$ molal.
$$
\left[\mathrm{K}_{\mathrm{b}}=0.52 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}\right]
$$
