Chemistry Transition Elements MDCAT 2013
PMDC Verified Question 63 of 68
Oxidation state of 'Fe' in \( K_{3}[Fe(CN)_{6}] \) is
A
+2
B
-6
C
-3
D
+3
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option D: +3
Concept:

The sum of the oxidation states of all atoms in a neutral complex must equal zero. The Potassium ion (\(K\)) is \(+1\) and the Cyanide ligand (\(CN\)) is \(-1\).

Solution:

  • Set up the algebraic equation for the neutral complex \(K_3[Fe(CN)_6]\):


  • \( 3(K) + Fe + 6(CN) = 0 \)


  • \( 3(+1) + Fe + 6(-1) = 0 \)


  • \( +3 + Fe - 6 = 0 \)


  • \( Fe - 3 = 0 \implies Fe = +3 \)


Why other options are incorrect:

  • Selecting \(+2\) would result from confusing this molecule with potassium ferrocyanide, \(K_4[Fe(CN)_6]\).

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