MCQ
Which complex is most stable ?

Where $kd =$ Dissociation constant

  • A
    $[Cu(CN)_2]^-; Kd = 1 \times 10^{-16}$
  • B
    $[Fe(CN)_6^-]^{-4} ; Kd = 1 \times 10^{-37}$
  • $[Fe(CN)_6]^{-3} ; Kd = 1 \times 10^{-44}$
  • D
    $[Ag(CN)_2]^-; Kd = 1 \times 10^{-20}$

Answer

Correct option: C.
$[Fe(CN)_6]^{-3} ; Kd = 1 \times 10^{-44}$
c
The stability constant or the dissociation constant is the equilibrium constant for the dissociation of the metal ligand bond. Higher is the stability constant, higher is the stability of the complex. The stability constant of $\left[ Fe ( CN )_{6}\right]^{3-}$ is $K _{d}=1 \times 10^{-44}$. It is minimum among the given
complexes. Hence, the complex $\left[ Fe ( CN )_{6}\right]^{3-}$ is most stable.

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