# Select the odd one w.r.t. EAN :- (1)    [Fe(CO)5] (2)    [Cr(CN)6]–3 (3)    [Mn2(CO)10] (4)    [Fe(CN)6]–4 ​Answer given is 2

Dear Student,

A coordination compound follows EAN rule if its effective atomic number is equal to the atomic number of the next noble gas.

Effective atomic number = Atomic number - Oxidation state + Coordination number x 2

The EAN for the given compounds are:

1. [Fe(CO)5]
Atomic number of Fe = 26, Oxidation state = 0, Coordination number = 5
So, EAN = 26 -0 +5x2 = 36
Thus, it follows EAN rule as it has EAN same as the atomic number of Xenon.

2. [Cr(CN)6]3-
Atomic number of chromium = 24, Oxidation state of Cr = -3 +6 = +3 , Coordination number = 6
EAN = 24 - 3 + 6 x 2 = 33
Since it does not have EAN same as the atomic number of Xe, it does not follow the EAN rule.

3. [Mn2(CO)10]
Atomic number for 2 x  Mn = 2 x 25 = 50 , Oxidation state = 0 , Coordination number = 10 + 1 for Mn-Mn bond = 11
EAN = 50 +11 x 2 = 72 for 2 x Mn
For 1 Mn, EAN = 72 x 0.5 = 36
Thus, it follows the EAN rule

4. [Fe(CN)6]4-
Atomic number of Fe = 26 , Oxidation state of Fe = +2 , Coordination number = 6
EAN = 26 -2 +6x2 = 36
Thus, it follows EAN rule.

Thus, compounds 1,3 and 5 have an EAN of 36 and follow EAN rule whereas compound 2 does not follow the rule.

Hence, compound 2 is the odd one out.

Hope it helps.

Regards

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