Calculate the solubility product of $\mathrm{C}{\mathrm{o}}_2\left[\mathrm{F}\mathrm{e}\right(\mathrm{C}\mathrm{N}{)}_6]$ in water at $25°$ C.
Given, conductivity of saturated solutions of $\mathrm{C}{\mathrm{o}}_2\left[\mathrm{F}\mathrm{e}\right(\mathrm{C}\mathrm{N}{)}_6]$ is $\text{2}\text{.06}\text{×}{\text{10}}^{-\text{6}}{\text{Ω}}^{-\text{1}}{\text{cm}}^{-\text{1}}$ and that of water used is $\text{4}\text{.1}\text{×}{\text{10}}^{-\text{7}}{\text{Ω}}^{-\text{1}}{\text{cm}}^{-\text{1}}$. The ionic molar conductivities of $\mathrm{C}{\mathrm{o}}^{2+}$ and $\left[\mathrm{F}\mathrm{e}\right(\mathrm{C}\mathrm{N}{)}_6{]}^{4-}$ are $\text{86}\text{.0}\text{Ω}{\text{cm}}^{\text{2}}{\text{mol}}^{-\text{1}}$ and $\text{444}\text{.0}{\text{Ω}}^{-\text{1}}{\text{cm}}^{\text{2}}{\text{mol}}^{-\text{1}}$, respectively.

• Correct answer
  A

  $\text{7}\text{.87}\text{×}{\text{10}}^{-\text{17}}$
• B

  $7.87\times 10^{-6}$
• C

  $7.87\times 10^{-8}$
• D

  $7.87\times 10^{-9}$

Hence, the correct answer is option: 'A'.