Chemistry Transition Elements ETEA 2019
PMDC Verified Question 50 of 68
In the complex, potassium hexacyanoferrate (III) \( K_{3}[Fe(CN)_{6}] \) the coordination number of Fe is:
A
9
B
3
C
6
D
d
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option C: 6
Concept:

The coordination number is defined as the number of coordinate covalent bonds formed between the ligands inside the square brackets (coordination sphere) and the central metal atom.

Solution:

  • Look exclusively at the complex ion inside the brackets: \([Fe(CN)_6]^{3-}\).


  • The central metal is Iron (\(Fe\)).


  • It is bonded to Cyanide (\(CN^-\)) ligands. Cyanide is a monodentate ligand, meaning each \(CN^-\) forms exactly one bond with the metal.


  • Since there are 6 \(CN^-\) ligands, there are 6 bonds. Therefore, the coordination number is 6.


Why other options are incorrect:

  • 3: This is the oxidation state of Fe in this complex, or the number of potassium ions, not the coordination number.


  • 9 / d: Random distractors.

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