The Crystal Field Stabilization Energy (CFSE) and magnetic moment (spin-only) of an octahedral aqua complex of a metal ion $\left(\mathrm{M}^{\mathrm{Z}+}\right)$ are $-0.8 \Delta_{0}$ and 3.87 BM, respectively. Identify $\left(\mathrm{M}^{\mathrm{Z}+}\right)$:

JEE Main · 2021 · 01 Sep 2021 · Shift 2 · Coordination Compounds

The Crystal Field Stabilization Energy (CFSE) and magnetic moment (spin-only) of an octahedral aqua complex of a metal ion

(M^{Z +})

are

- 0.8 Δ_{0}

and 3.87 BM, respectively. Identify

(M^{Z +})

(A) $Cr^{3 +}$
(B) $Mn^{4 +}$
(C) $V^{3 +}$
(D) $Co^{2 +}$ ✓ Correct

Answer: (D)

Solution

A spin-only moment of

3.87 BM

means

μ = n (n + 2)

with

n = 3

unpaired electrons. Water is a weak-field ligand, so the complex is high-spin. A

3 d^{7}

ion then takes the configuration

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

, with three unpaired electrons and

CFSE = (- 0.4 \times 5 + 0.6 \times 2) Δ_{0} = - 0.8 Δ_{0}

, matching both data. The

3 d^{7}

aqua ion is

C o^{2 +}

JEE Main · 2021 · 01 Sep 2021 · 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 →