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JEE Main Chemistry Coordination Compounds 2026 JEE Main 2026 (21 January Shift 1)

JEE Main Chemistry Question (2026) — Solution

Question

Given below are two statements : Statement I : Among . [ Cu ( NH _ 3 )_ 4 ]^ 2+ , [ Ni ( en )_ 3 ) ]^ 2+ , [ Ni ( NH _ 3 )_ 6 ]^ 2+ and [ Mn ( H _ 2 O )_ 6 ]^ 2+ , [ Mn ( H _ 2 O )_ 6 ]^ 2+ has the maximum number of unpaired electrons. Statement II : The number of pairs among \ [ NiCl _ 4 ]^ 2- , [ Ni ( CO )_ 4 ] \ , \ [ NiCl _ 4 ]^ 2- , [ Ni ( CN )_ 4 ]^ 2- \ and \ [ Ni ( CO )_ 4 ], [ Ni ( CN )_ 4 ]^ 2- \ that contain only diamagnetic species is two. In the light of the above statements, choose the correct answer from the options given below : Statement I is true but Statement II is false Both Statement I and Statement II are false

Options

  1. A. Statement I is true but Statement II is false
  2. B. Both Statement I and Statement II are false
  3. C. Both Statement I and Statement II are true
  4. D. Statement I is false but Statement II is true

Answer

A. Statement I is true but Statement II is false

Step-by-step solution

Statement I: Unpaired electrons in each complex: [Cu(NH_3)_4]^ 2+ : Cu^ 2+ is d^9 → 1 unpaired [Ni(en)_3]^ 2+ : Ni^ 2+ is d^8, octahedral → 2 unpaired [Ni(NH_3)_6]^ 2+ : Ni^ 2+ is d^8 → 2 unpaired [Mn(H_2O)_6]^ 2+ : Mn^ 2+ is d^5, weak field → high spin → 5 unpaired [Mn(H_2O)_6]^ 2+ has maximum. Statement I is true. Statement II: [NiCl_4]^ 2- : Ni^ 2+ (d^8), tetrahedral → paramagnetic [Ni(CO)_4]: Ni^0 (d^ 10 ) → diamagnetic [Ni(CN)_4]^ 2- : Ni^ 2+ (d^8), square planar → diamagnetic Only pair \ [Ni(CO)_4], [Ni(CN)_4]^ 2- \ has both diamagnetic. Count = 1, not 2. Statement II is false.

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