QJEEM21Che2fe: JEE Main 2021 Chemistry - Class 12 JEEM21Che2fe Solution: If a compound AB dissociates to the extent of 75% in an aqueous …

As AB is a binary electrolyte,

$\therefore$ AB $\rightleftharpoons$ A⁺ + B ^$-$ , n = 2

$i = 1 + \alpha (n - 1) = 1 + {{75} \over {100}}(2 - 1) = 1.75$

Given, $\Delta$ T_b = 2.5 K

K_b = 0.52 K kg mol ^{$-$ 1}

$\therefore$ $\Delta$ T_b = K_b $\times$ m $\times$ i

$\Rightarrow m = {{\Delta {T_b}} \over {{K_b} \times i}} = {{2.5} \over {0.52 \times 1.75}}$

$= 2.74 \simeq 3$ mol/kg