JEE Main · 2020 · 04 Sep 2020 · Shift 1 · Coordination Compounds

The pair in which both the species have the same magnetic moment (spin only) is:

(A) $[Co (OH)_{4}]^{2 -}$ and $[Fe (NH_{3})_{6}]^{2 +}$
(B) $[Mn (H_{2} O)_{6}]^{2 +}$ and $[Cr (H_{2} O)]^{2 +}$
(C) $[Cr (H_{2} O)_{6}]^{2 +}$ and $[Fe (H_{2} O)_{6}]^{2 +}$ ✓ Correct
(D) $[Cr (H_{2} O)_{6}]^{2 +}$ and $[CoCl_{4}]^{2 -}$

Answer: (C)

Solution

The spin-only moment depends only on the number of unpaired electrons. With water as a weak-field ligand,

Cr X^{2 +}

(

3 d^{4}

) keeps

4

unpaired electrons and

Fe X^{2 +}

(

3 d^{6}

) also has

4

unpaired electrons. Both

[Cr (H X_{2} O) X_{6}] X^{2 +}

and

[Fe (H X_{2} O) X_{6}] X^{2 +}

therefore have the same moment,

μ = 4 (4 + 2) = 24 \approx 4.9

BM, so this is the pair with equal magnetic moments.

JEE Main · 2020 · 04 Sep 2020 · Shift 1 · 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 →