The solubility product of a sparingly soluble salt A _ 2 X _ 3 is 1...

${K}_{sp}\left({A}_{2}{X}_{3}\right) = 1 . 1 \times {10}^{- 23} = 110 \times {10}^{- 25}$

${K}_{sp} = {\left(2\right)}^{2}{\left(3\right)}^{3}{\left(s\right)}^{5} = 110 \times {10}^{- 25}$

$4 \times 27{\left(s\right)}^{5} = 110 \times {10}^{- 25}; S = M = 1 \times {10}^{- 5}$

$K = 3 \times 10 - 5{Sm}^{- 1}$

${\lambda}_{m} = \left[x\right] \times {10}^{- 3}{Sm}^{2}{mol}^{- 1}$

${\lambda}_{m} = \left[\dfrac{K \times {10}^{- 3}}{M}\right]$

$= \dfrac{3 \times {10}^{- 5} \times {10}^{- 3}}{1 \times {10}^{- 5}} = 3 \times {10}^{- 3}{Sm}^{2}{mol}^{- 1}$