JEE Main 2026 Jan 21 Shift 2, Chemistry Q24: Colour, Magnetism And Stability Of Co-ordination Compounds

JEE Main2026Jan 21, Shift 2Chemistry

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 those metal ions is __________.

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Solution

For high-spin octahedral complexes, count d-electrons and find $n$ (unpaired) for each ion:

V $^{3 +}$ : $d^{2}$ → $n = 2$ , $μ = 8 \approx 2.83$ BM.

Ti $^{2 +}$ : $d^{2}$ → $n = 2$ , $μ \approx 2.83$ BM.

Ni $^{2 +}$ : $d^{8}$ → $n = 2$ , $μ \approx 2.83$ BM.

Fe $^{2 +}$ : $d^{6}$ → $n = 4$ , $μ = 24 \approx 4.90$ BM.

Co $^{2 +}$ : $d^{7}$ → $n = 3$ , $μ = 15 \approx 3.87$ BM.

Only Fe $^{2 +}$ and Co $^{2 +}$ have $μ > 3.0$ BM. Sum of their unpaired electrons $= 4 + 3 = 7$ .

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JEE Main 2026 Jan 21 Shift 2, Chemistry Q24: Colour, Magnetism And Stability Of Co-ordination Compounds

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