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Spin-only magnetic moment or number of unpaired electrons of a given complex

This type of question, asked 19 times: 2021 Paper 2, 2021 Paper 12, 2021 Paper 13, 2021 Paper 23, 29 Jun 2022, 26 Jul 2022, 27 Jul 2022, 1 Feb 2023, 6 Apr 2023, 8 Apr 2023, 11 Apr 2023, 27 Jan 2024, 31 Jan 2024, 4 Apr 2024, 8 Apr 2024, 29 Jan 2025, 7 Apr 2025, 23 Jan 2026 S2, 4 Apr 2026 S1. All 20 questions below, oldest first.

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  1. Question 1

    2021 Paper 2

    42
    The calculated magnetic moments (spin only value) for species [FeCl4]2−,[Co(C2O4)3]3−\left\lbrack FeCl_{4} \right\rbrack^{2 -},\left\lbrack Co\left( C_{2}O_{4} \right)_{3} \right\rbrack^{3 -} and MnO42−MnO_{4}^{2 -} respectively are :

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  2. Question 2

    2021 Paper 12

    36
    Spin only magnetic moment of Fe2+Fe^{2 +} with weak field ligand is:

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  3. Question 3

    2021 Paper 13

    35
    Total number of unpaired electrons in [Co(NH3)6]Cl2\left\lbrack Co\left( NH_{3} \right)_{6} \right\rbrack Cl_{2} and [Co(NH3)6]Cl3\left\lbrack Co\left( NH_{3} \right)_{6} \right\rbrack Cl_{3}, respectively, are

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  4. Question 4

    2021 Paper 23

    40
    Spin only magnetic moment in BM of [Fe(CO)4(C2O4)]+\left\lbrack Fe(CO)_{4}\left( C_{2}O_{4} \right) \right\rbrack^{+}is:

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  5. Question 5

    29 Jun 2022

    146
    Spin only magnetic moment of [MnBr6]4−\left\lbrack MnBr_{6} \right\rbrack^{4 -} is ____ B.M. (round off to the closest integer)

  6. Question 6

    26 Jul 2022

    59
    The difference between spin only magnetic moment values of [Co(H2O)6]Cl2\left\lbrack Co\left( H_{2}O \right)_{6} \right\rbrack Cl_{2} and [Cr(H2O)6]Cl3\left\lbrack Cr\left( H_{2}O \right)_{6} \right\rbrack Cl_{3} is

  7. Question 7

    27 Jul 2022

    149
    The spin only magnetic moment of the complex present in Fehling's reagent is ____ B.M. (Nearest integer).

  8. Question 8

    1 Feb 2023

    145
    The spin only magnetic moment of [Mn(H2O)6]2+\left\lbrack Mn\left( H_{2}O \right)_{6} \right\rbrack^{2 +} complexes is___ B.M. (Nearest integer) (Given: Atomic no. of MnMn is 25)

  9. Question 9

    6 Apr 2023

    43
    Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R. Assertion A: The spin only magnetic moment value for [Fe(CN)6]3−\left\lbrack Fe(CN)_{6} \right\rbrack^{3 -} is 1.74BM1.74BM, whereas for [Fe(H2O)6]3+\left\lbrack Fe\left( H_{2}O \right)_{6} \right\rbrack^{3 +} is 5.92BM5.92BM. Reason RR : In both complexes, FeFe is present in +3 oxidation state. In the light of the above statements, choose the correct answer from the options given below:

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  10. Question 10

    8 Apr 2023

    131
    Match List I with List II :-
    ------------------ List I Coordination Complex --------------------------------- List II Number of unpaired electrons ---------------
    (A)
    [Cr(CN)6]3−\left\lbrack Cr(CN)_{6} \right\rbrack^{3 -}
    		(I)0
    (B)
    [Fe(H2O)6]2+\left\lbrack Fe\left( H_{2}O \right)_{6} \right\rbrack^{2 +}
    		(II)3
    (C)
    [Co(NH3)6]3+\left\lbrack Co\left( NH_{3} \right)_{6} \right\rbrack^{3 +}
    		(III)2
    (D)
    [Ni(NH3)6]2+\left\lbrack Ni\left( NH_{3} \right)_{6} \right\rbrack^{2 +}
    		(IV)4
    Choose the correct answer from the options given below:

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  11. Question 11

    11 Apr 2023

    52
    The ratio of spin-only magnetic moment values μeff [Cr(CN)6]3−/μeff [Cr(H2O)6]3+\mu_{\text{eff~}}\left\lbrack Cr(CN)_{6} \right\rbrack^{3 -}/\mu_{\text{eff~}}\left\lbrack Cr\left( H_{2}O \right)_{6} \right\rbrack^{3 +} is____

  12. Question 12

    11 Apr 2023

    138
    The magnetic moment is measured in Bohr Magneton (BM). Spin only magnetic moment of FeFe in [Fe(H2O)6]3+\left\lbrack Fe\left( H_{2}O \right)_{6} \right\rbrack^{3 +} and [Fe(CN)6]3−\left\lbrack Fe(CN)_{6} \right\rbrack^{3 -} complexes respectively is :

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  13. Question 13

    27 Jan 2024

    144
    The Spin only magnetic moment value of square planar complex [Pt(NH3)2Cl(NH2CH3)]Cl\left\lbrack Pt\left( NH_{3} \right)_{2}Cl\left( NH_{2}CH_{3} \right) \right\rbrack Cl is ______ B.M. (Nearest integer) (Given atomic number for Pt=78Pt = 78 )

  14. Question 14

    31 Jan 2024

    52
    The 'Spin only' Magnetic moment for [Ni(NH3)6]2+\left\lbrack Ni\left( NH_{3} \right)_{6} \right\rbrack^{2 +} is _____ ×10−1BM\times10^{- 1}BM. (given == Atomic number of Ni:28Ni:28 )

  15. Question 15

    4 Apr 2024

    38
    Number of complexes from the following with even number of unpaired "d" electrons is . [V(H2O)6]3+, [Cr(H2O)6]2+, [Fe(H2O)6]3+\left\lbrack V\left( H_{2}O \right)_{6} \right\rbrack^{3 +},\ \left\lbrack Cr\left( H_{2}O \right)_{6} \right\rbrack^{2 +},\ \left\lbrack Fe\left( H_{2}O \right)_{6} \right\rbrack^{3 +}, [Ni(H2O)6]3+,[Cu(H2O)6]2+\left\lbrack Ni\left( H_{2}O \right)_{6} \right\rbrack^{3 +},\left\lbrack Cu\left( H_{2}O \right)_{6} \right\rbrack^{2 +} [Given atomic numbers: V=23,Cr=24,Fe=26V = 23,Cr = 24,Fe = 26, Ni=28,Cu=29]Ni = 28,Cu = 29\rbrack

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  16. Question 16

    8 Apr 2024

    148
    Total number of unpaired electrons in the complex ion [Co(NH3)6]3+\left\lbrack Co\left( NH_{3} \right)_{6} \right\rbrack^{3 +} and [NiCl4]2−\left\lbrack NiCl_{4} \right\rbrack^{2 -} is

  17. Question 17

    29 Jan 2025

    101
    The calculated spin-only magnetic moments of K3[Fe(OH)6]K_{3}\left\lbrack Fe(OH)_{6} \right\rbrack and K4[Fe(OH)6]K_{4}\left\lbrack Fe(OH)_{6} \right\rbrack respectively are :

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  18. Question 18

    7 Apr 2025

    114
    The number of unpaired electrons responsible for the paramagnetic nature of the following complex species are respectively :
    [Fe(CN)6]3−,[FeF6]3−,[CoF6]3−,[Mn(CN)6]3−\left\lbrack Fe(CN)_{6} \right\rbrack^{3 -},\left\lbrack FeF_{6} \right\rbrack^{3 -},\left\lbrack CoF_{6} \right\rbrack^{3 -},\left\lbrack Mn(CN)_{6} \right\rbrack^{3 -}

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  19. Question 19

    23 Jan 2026 S2

    49
    Total number of unpaired electrons present in the central metal atoms/ions of [Ni(CO)4],[NiCl4]2−,[PtCl2(NH3)2],[Ni(CN)4]2−\left\lbrack Ni(CO)_{4} \right\rbrack,\left\lbrack {NiCl}_{4} \right\rbrack^{2 -},\left\lbrack {PtCl}_{2}\left( {NH}_{3} \right)_{2} \right\rbrack,\left\lbrack Ni(CN)_{4} \right\rbrack^{2 -} and [Pt(CN)4]2−\left\lbrack Pt(CN)_{4} \right\rbrack^{2 -} is ____\_\_\_\_ .

  20. Question 20

    4 Apr 2026 S1

    37
    Match List-I with List-II
    List-I Complex ionList-II Calculated spin only magnetic moment (BM)
    (A)
    [Cr(H2O)6]2+\left\lbrack Cr\left( H_{2}O \right)_{6} \right\rbrack^{2 +}
    		(I)3.87
    (B)
    [Co(H2O)6]2+\left\lbrack Co\left( H_{2}O \right)_{6} \right\rbrack^{2 +}
    		(II)5.92
    (C)
    [Cu(H2O)6]2+\left\lbrack Cu\left( H_{2}O \right)_{6} \right\rbrack^{2 +}
    		(III)4.90
    (D)
    [Mn(H2O)6]2+\left\lbrack Mn\left( H_{2}O \right)_{6} \right\rbrack^{2 +}
    		(IV)1.73
    Choose the correct answer from the options given below:

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