Question

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
A ⇒ Spin only magnetic moment of [Fe(CN)₆]^–3 is 1.73 B.M. and [Fe(H₂O)₆]⁺³ is 5.92 B.M.
R ⇒ In both cases Fe have +3 oxidation state
In the light of the above statements, write the detailed answer:

Answer 1

[Fe(CN)₆]^–3 : Fe⁺³ : 3d⁵ with S.F.L 
$⇒ n = 1$
Magnetic moment = $1.73$ B.M [Fe(H₂O)₆]⁺³ Fe⁺³ : 3d⁵ with W.F.L 
$⇒ n = 5$
Magnetic moment = $5.92$ B.M 

$\text{Both A \& R are correct but R is not the correct explanation }$

Answer 2

The magnetic moment of $[Fe(H_2O)_6]^{3+}$ is 5.92 BM because it has high-spin Fe³⁺ (d⁵, S = $\frac{5}{2}$) and it has five unpaired electrons. 
On the other hand, $[Fe(CN)_6]^{3-}$ has low-spin Fe³⁺ (d⁵, S = $\frac{1}{2}$) and only one unpaired electron. 
Therefore, the magnetic moment of $[Fe(CN)_6]^{3-}$ is 1.73 BM, which is much lower than that of $[Fe(H_2O)_6]^{3+}$. 
$\text{The oxidation state of Fe in both complexes is indeed +3.}$