Question

What is the Effective Atomic Number (EAN) of $[Fe(CN)_6]^{4-}$?

• A. 34
• B. 36
• C. 38
• D. 40

Hint:

For coordination compounds:
EAN = Atomic number – Oxidation state + electrons donated by ligands.

Answer 1

The Correct Option is B

Concept:
The Effective Atomic Number (EAN) rule states that a metal atom in a coordination compound tends to achieve the electronic configuration of the nearest noble gas after accepting electrons from ligands. \[ \text{EAN} = Z - \text{oxidation state} + \text{electrons donated by ligands} \] where \(Z\) is the atomic number of the metal.

Step 1: Determine the atomic number of iron
Iron (\(Fe\)) has atomic number: \[ Z = 26 \]

Step 2: Determine oxidation state of iron
Each \(CN^-\) ligand carries a charge of \(-1\). In \(Fe(CN)_6^{4-}\): \[ x + 6(-1) = -4 \] \[ x - 6 = -4 \] \[ x = +2 \] So iron is in the \(+2\) oxidation state.

Step 3: Calculate electron donation from ligands
Each \(CN^-\) ligand donates 2 electrons. \[ 6 \times 2 = 12 \text{ electrons} \]

Step 4: Apply the EAN formula \[ EAN = 26 - 2 + 12 \] \[ EAN = 36 \] Conclusion:
The Effective Atomic Number of \(Fe(CN)_6^{4-}\) is \(\mathbf{36}\), which corresponds to the noble gas configuration of krypton.