Question

The equilibrium constants for the two complex formation are :

$4K^{+}+Fe{\left(CN\right)}_6^{4-}⟶K_4\left[Fe{\left(CN\right)}_6\right];K=3.8\times {10}^{-38}$

$3K^{+}+Fe{\left(CN\right)}_6^{3-}⟶K_3\left[Fe{\left(CN\right)}_6\right];K=5\times {10}^{-18}$

• A. $K_{4}Fe{\left(CN\right)}_6$ is more stable
• B. $K_{3}Fe{\left(CN\right)}_6$ is more stable
• C. both are equally stable
• D. stability of complexes cannot be decrease

Answer 1

Answer: (B)

$K_{3}Fe{\left(CN\right)}_6$ is more stable

Higher is formation constant, lesser is dissociation constant of complex more is stability.

$\text{Stability}\propto \frac{1}{\text{Dissociation constant of complex}}$

or

$\text{Stability}\propto \frac{1}{\text{Formation constant of complex}}$
As the value of formation constant of $K_{3}Fe{\left(CN\right)}_6$ is more, hence it is more stable.

Therefore, option B is correct.