Assertion (A): The formation constant of $[Fe (CN)_{6}]^{3 -}$ is much higher than that of $[Fe (CN)_{6}]^{4 -}$ .
Reason (R): $Fe^{3 +}$ has higher charge and smaller size than $Fe^{2 +}$ hence stronger attraction for
$CN^{-}$ ligands.

Question

Assertion (A): The formation constant of $[Fe (CN)_{6}]^{3 -}$ is much higher than that of $[Fe (CN)_{6}]^{4 -}$ .

Reason (R): $Fe^{3 +}$ has higher charge and smaller size than $Fe^{2 +}$ hence stronger attraction for

$CN^{-}$ ligands.

TestHub · Accepted Answer

Question Explanation: Stability of coordination compounds based on charge and size.

Concept: Factors affecting the stability of complexes.

Solution: The stability (formation constant) of a coordination complex depends on the charge density of the central metal ion.

Charge density $\propto \frac{Charge}{Radius}$

Since Charge: $Fe^{3 +} > Fe^{2 +}$ and Size: $Fe^{3 +} < Fe^{2 +}$

This higher charge-to-size ratio leads to a stronger electrostatic attraction for the $CN^{-}$ ligands, making $[Fe (CN)_{6}]^{3 -}$ more stable than $[Fe (CN)_{6}]^{4 -}$ .

Final Answer: Option (A)

Chemistry - Coordination Chemistry Question with Solution | TestHub

Options:

Doubts & Discussion

JEE Main 2027 (Class 12)