Question:

Metal carbonyls can have formula M(CO)\(_x\) where \(x =\) number of CO units coordinated to metal M. What is the formula of the carbonyl of Fe (26) if EAN of Fe in metal carbonyl is 36?

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EAN rule (18-electron rule): Most stable carbonyls have total electrons = 36 (for 4th period metals).
Updated On: Apr 23, 2026
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The Correct Option is D

Solution and Explanation

Step 1: Understanding the Concept:
EAN (Effective Atomic Number) = Atomic number - (oxidation state) + 2 \(\times\) (number of ligands). CO is neutral ligand.
Step 2: Detailed Explanation:
For Fe(CO)\(_x\) in zero oxidation state: EAN = 26 + 2x = 36 \(\Rightarrow\) 2x = 10 \(\Rightarrow\) x = 5.
Formula = Fe(CO)\(_5\). Iron pentacarbonyl.
Step 3: Final Answer:
Thus, \(x = 5\).
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