Q. Which of following coordinate complexes is an exception to EAN rule?
(Given Atomic number Pt = 78, Fe = 26, Zn = 30, Cu = 29)

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A

$\left[\right.Pt\left(\right.NH_{3}\left(\left.\right)_{6}\left(\left]\right.\right)^{4 +}$

B

$\left[\right.Fe\left(\right.CN\left(\left.\right)_{6}\left(\left]\right.\right)^{4 -}$

C

$\left[\right.Zn\left(\right.NH_{3}\left(\left.\right)_{4}\left(\left]\right.\right)^{2 +}$

D

$\left[\right.Cu\left(\right.H_{2}O\left(\left.\right)_{4}\left(\left]\right.\right)^{2 +}$

Solution:

As in $\left[\right.Cu\left(\right.H_{2}O\left(\left.\right)_{4}\left(\left]\right.\right)^{2 +}$ EAN is 35, so it does not follow EAN rule.
EAN $=$ Atomic number of central atom + Number of electrons donated by ligands - oxidation state of central atom.
(A) $\left[\right.Pt\left(\right.NH_{3}\left(\left.\right)_{6}\left(\left]\right.\right)^{4 +}$ EAN $=78+2\times 6-4=86$
(B) $\left[\right.Fe\left(\right.CN\left(\left.\right)_{6}\left(\left]\right.\right)^{4 -}$ EAN $=26+1\times 6+4=36$
(C) $\left[\right.Zn\left(\right.NH_{3}\left(\left.\right)_{4}\left(\left]\right.\right)^{2 +}$ EAN $=30+2\times 4-2=36$
(D) $\left[\right.Cu\left(\right.H_{2}O\left(\left.\right)_{4}\left(\left]\right.\right)^{2 +}$ EAN $=29+2\times 4-2=35$

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