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ChemistryJEE Main 24 Jan 2026, Shift 1·Q1·MCQ·Moderate

Coordination Compounds · Valence bond theory magnetic moment

Given below are two statements :

Statement-I Hybridisation, shape and spin only magnetic moment of KX3[Co(COX3)X3]\ce{K3[Co(CO3)3]} are sp3^3d2^2, octahedral and 4.9 BM respectively.

Statement-II Geometry, hybridisation and spin only magnetic moment values (BM) of the ions [Ni(CN)X4]X2−\ce{[Ni(CN)4]^{2-}}, [MnBrX4]X2−\ce{[MnBr4]^{2-}} and [CoFX6]X3−\ce{[CoF6]^{3-}} respectively are square planar, tetrahedral, octahedral : dsp2^2, sp3^3, sp3^3d2^2 and 0, 5.9, 4.9.

In the light of the above statements, choose the correct answer from the options given below

  1. (1)Both statement-I and statement-II are false
  2. (2)Statement I is false but statement-II is true
  3. (3)Both statement-I and statement-II are true
  4. (4)Statement-I is true but statement-II is false
We corrected a printing error in the original paper

Answer corrected; the source key is (3) — [Co(COX3)X3]X3−\ce{[Co(CO3)3]^{3-}} is a low-spin Co(III) (d6^6) complex like [Co(CX2OX4)X3]X3−\ce{[Co(C2O4)3]^{3-}}: d2^2sp3^3, diamagnetic (0 BM), so Statement-I is false and Statement-II is true; also source printed “spin only magnetic moment of KX3[Co(COX3)X3]\ce{K3[Co(CO3)3]} is”.

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See the full 24 Jan 2026, Shift 1 paper