The correct increasing order of spin only magnetic moment values of the complex ions \(\text{ }{\left[{\mathrm{MnBr}}_{4}\right]}^{2−}\left(\mathrm{A}\right),\text{ }{\left[\mathrm{Cu}\left({\mathrm{H}}_{2}{\mathrm{O}}_{6}\right)\right]}^{2+}\text{ }\left(\mathrm{B}\right),\text{ }{\left[\mathrm{Ni}{\left(\mathrm{CN}\right)}_{4}\right]}^{2−}\text{ }\)(C) and \(\text{ }{\left[\mathrm{Ni}{\left({\mathrm{H}}_{2}\mathrm{O}\right)}_{6}\right]}^{2+}\left(\mathrm{D}\right)\) is:

[JEE Main 2026, 28 Jan (Shift 2)]

Question

The correct increasing order of spin only magnetic moment values of the complex ions \(\text{ }{\left[{\mathrm{MnBr}}_{4}\right]}^{2−}\left(\mathrm{A}\right),\text{ }{\left[\mathrm{Cu}\left({\mathrm{H}}_{2}{\mathrm{O}}_{6}\right)\right]}^{2+}\text{ }\left(\mathrm{B}\right),\text{ }{\left[\mathrm{Ni}{\left(\mathrm{CN}\right)}_{4}\right]}^{2−}\text{ }\)(C) and \(\text{ }{\left[\mathrm{Ni}{\left({\mathrm{H}}_{2}\mathrm{O}\right)}_{6}\right]}^{2+}\left(\mathrm{D}\right)\) is:

[JEE Main 2026, 28 Jan (Shift 2)]

YESPYQ · Accepted Answer

Correct answer: b) C < B < D < A. (C) [Ni(CN)₄]²⁻ Ni²⁺ → 3d⁸ CN⁻ = strong field ligand → pairing occurs Structure: square planar Unpaired electrons = 0 (B) [Cu(H₂O)₆]²⁺ Cu²⁺ → 3d⁹ Unpaired electrons = 1 (D) [Ni(H₂O)₆]²⁺ Ni²⁺ → 3d⁸ H₂O = weak field → no pairing Unpaired electrons = 2 (A) [MnBr₄]²⁻ Mn²⁺ → 3d⁵ Br⁻ = weak field Tetrahedral → no pairing Unpaired electrons = 5 Order (increasing) C (0) < B (1) < D (2) < A (5)

The correct increasing order of spin only magnetic moment values of the complex ions \(\text{ }{\left[{\mathrm{MnBr}}_{4…

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