If an iron (III) complex with the formula $\left[\mathrm{Fe}\left(\mathrm{NH}_{3}\right)_{\mathrm{x}}(\mathrm{CN})_{\mathrm{y}}\right]^{-}$has no electron in its $\mathrm{e}_{\mathrm{g}}$ orbital, then the value of $\mathrm{x}+\mathrm{y}$ is

JEE Main · 2024 · 04 Apr 2024 · Shift 2 · Coordination Compounds

If an iron (III) complex with the formula

[Fe (NH_{3})_{x} (CN)_{y}]^{-}

has no electron in its

e_{g}

orbital, then the value of

x + y

(A)5
(B)6✓ Correct
(C)3
(D)4

Answer: (B)

Solution

For the

e_{g}

orbitals to be completely empty in an octahedral Fe(III) (

d^{5}

) complex, the ion must be low-spin:

t_{2 g}^{5} e_{g}^{0}

. This requires a sufficiently strong field, provided here by the

C N^{-}

ligands (a strong-field ligand), while

N H_{3}

is comparatively weak.
Charge balance for

[F e (N H_{3})_{x} (C N)_{y}]^{-}

with

F e^{3 +}

3 + 0 (x) - y = - 1 \Rightarrow y = 4

, and for an octahedral complex

x + y = 6 \Rightarrow x = 2

.
So

x = 2

y = 4

, and

x + y = 6

JEE Main · 2024 · 04 Apr 2024 · Shift 2 · Single correct option

Practise more: all JEE Main PYQs on Coordination Compounds →

More JEE Main questions on Coordination Compounds

Given below are two statements:

Statement I: Among $[Cu (NH_{3})_{4}]^{2 +}$ , $[Ni (en)_{3}]^{2 +}$ , $[Ni (NH_{3})_{6}]^{2 +}$ and $[Mn (H_{2} O)_{6}]^{2 +}$ , …
JEE Main 2026View solution →
Consider the transition metal ions $Mn^{3 +}, Cr^{3 +}, Fe^{3 +}$ and $Co^{3 +}$ and all form low spin octahedral complexes. The correct decreasing order of unpaired electrons in their respective d-orbitals of the complexes is
JEE Main 2026View solution →
A first row transition metla (M) does not liberate $H_{2}$ gas from dilute HCl .1 mol of aqueous solution of $MSO_{4}$ is treated with excess of aqueous KCN and then $H_{2} S (g)$ is passed through the solution. The amount of MS …
JEE Main 2026View solution →
Given below are two statements:

Statement I: Crystal Field Stabilization Energy (CFSE) of $[Cr (H_{2} O)_{6}]^{2 +}$ is greater than that of $[Mn (H_{2} O)_{6}]^{2 +}$ .

Statement II: Pot …
JEE Main 2026View solution →
Identify the metal ions among $Co^{2 +}$ , $Ni^{2 +}$ , $Fe^{2 +}$ , $V^{3 +}$ and $Ti^{2 +}$ having a spin-only magnetic moment value more than 3.0 BM. The sum of unpaired electrons present in the high spin octahedral complexes formed by thos …
JEE Main 2026View solution →
$[Ni (PPh_{3})_{2} Cl_{2}]$ is a paramagnetic complex. Identify the INCORRECT statements about this complex.
A. The complex exhibits geometrical isomerism.
B. The complex is white in colour.
C. The calculated spin-only magnetic moment of the complex is 2. …
JEE Main 2026View solution →