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JEE Main Chemistry Coordination Compounds 2026 JEE Main 2026 (28 January Shift 2)

JEE Main Chemistry Question (2026) — Solution

Question

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

  1. A. C = D < B < A
  2. B. C < B < D < A
  3. C. A = B < D < C
  4. D. A=B < C < D

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) = 8 2.83 BM. Increasing order: C (0) < B (1.73) < D (2.83) < A (5.92)

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