JEE Main202628 January 2026Evening ShiftChemistryCoordination CompoundsActual
The correct increasing order of spin-only magnetic moment values of the complex ions [ MnBr ₄ ]²⁻( A ), [ Cu ( H ₂ O )₆ ]²⁺( B ), [ Ni ( CN )₄ ]²⁻( C ) and [ Ni ( H ₂ O )₆ ]²⁺( D ) is :
Options
- AC = D < B < A
- BC < B < D < A
- CA = B < D < C
- DA=B < C < D
Correct answer
B. C < B < D < A
Step-by-step solution
Calculate spin-only magnetic moment using _s = n(n+2) where n is the number of unpaired electrons. For [ MnBr ₄]²⁻ (A): Mn(II) in tetrahedral environment is high spin with 5 unpaired electrons. _s = 5(7) = 35 5.92 BM. For [ Cu ( H ₂ O )₆]²⁺ (B): Cu(II) has 1 unpaired electron. _s = 1(3) = 3 1.73 BM. For [ Ni ( CN )₄]²⁻ (C): Ni(II) in square planar geometry is low spin with 0 unpaired electrons. _s = 0 BM. For [ Ni ( H ₂ O )₆]²⁺ (D): Ni(II) in octahedral environment is high spin with 2 unpaired electrons. _s = 2(4)