Coordination Chemistry: IIT JAM Practice SetBased on Previous Year Questions
1. The correct order of the 10Dq value (crystal field splitting) for the following complexes is:
A) [Co(H2 O)6 ]3+ < [Rh(H2 O)6 ]3+ < [Ir(H2 O)6 ]3+ 2 O)6 ]3+ < [Rh(H2 O)6 ]3+ < [Co(H2 O)6 ]3+ 2 O)6 ]3+ < [Co(H2 O)6 ]3+ < [Ir(H2 O)6 ]3+
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Answer: A (Splitting increases down the group 3d < 4d < 5d due to better metal-ligand overlap).
2. Which of the following ions is expected to show the highest Jahn-Teller distortion?
A) High spin Cr2+ (d4 )2+ (d5 )3+ (d6 )2+ (d8 )
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Answer: A (Asymmetric filling of eg orbitals (t2g 3 eg 1 ) leads to strong distortion).
3. The number of possible isomers (including stereoisomers) for the complex [Co(en)2 Cl2 ]+ is:
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Answer: 3 (1 trans-isomer which is optically inactive, and a pair of enantiomers for the cis-isomer).
4. The spin-only magnetic moment (in B.M.) of [FeF6 ]3- is approximately:
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Answer: 5.92 B.M. (Fe3+ is high spin d5 , n=5, μ = √[5(5+2)] = √35).
5. Which set of ligands is arranged in increasing order of field strength (Spectrochemical series)?
A) I- < Cl- < H2 O < NH3 < CN- - < NH3 < H2 O < Cl- < I- 3 < H2 O < I- < CN-
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Answer: A (Based on spectrochemical series experimental data).
6. The CFSE (in Δo ) for a d4 high spin octahedral complex is:
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Answer: -0.6 Δo (Electronic config: t2g 3 eg 1 . Calculation: 3 × (-0.4) + 1 × (0.6) = -0.6).
7. The coordination number and oxidation state of Cr in K3 [Cr(C2 O4 )3 ] are:
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Answer: CN = 6, OS = +3 (Oxalate is a bidentate ligand; 3 × 2 = 6).
8. Which of the following is an outer orbital complex?
A) [Fe(CN)6 ]3- 2 O)6 ]3+ 3 )6 ]3+
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Answer: B (H2 O is a weak field ligand, resulting in high spin sp3 d2 hybridization using 4d orbitals).
9. The geometry of [Ni(CN)4 ]2- and [NiCl4 ]2- are respectively:
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Answer: Square planar (dsp2 ) and Tetrahedral (sp3 ).
10. An octahedral complex [ML6 ]n+ is diamagnetic. If L is a strong field ligand, the metal ion M could be:
A) Cr3+ (d3 )3+ (d6 )3+ (d5 )
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Answer: B (Low spin d6 in octahedral field has all electrons paired in t2g orbitals).
11. The intensity of color in [MnO4 ]- is much higher than in [Mn(H2 O)6 ]2+ because of:
A) d-d transition
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Answer: B (Permanganate has Mn in +7 state (d0 ); color arises from LMCT which is Laporte and spin allowed).
12. For a tetrahedral complex, the relationship between Δt and Δo is:
A) Δt = 4/9 Δo t = 9/4 Δo t = 1/2 Δo
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Answer: A (Due to fewer ligands and less effective orbital overlap).
13. Which of the following does NOT follow the 18-electron rule?
A) [Fe(CO)5 ]6 ]6 ]4 ]
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Answer: C (Vanadium has 5 valence e- + 12 from CO = 17 electrons).
14. The ground state term symbol for a d2 metal ion is:
A) 3 F3 P1 D
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Answer: A (According to Hund's Rule for maximum multiplicity and L value).
15. The number of possible geometrical isomers for the octahedral complex [Ma2 b2 c2 ] is:
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Answer: 5 (All-cis, All-trans, and various combinations of cis-trans).
16. According to the Orgel diagram, a d1 octahedral complex will show how many electronic transitions?
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Answer: One (2 T2g → 2 Eg ).
17. Which of the following is a 'pi-acid' ligand?
A) NH3 - 2 O
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Answer: B (Carbon monoxide can accept electrons from metal into its π* orbitals).
18. A complex [M(H2 O)6 ]Cl2 has a magnetic moment of 3.87 B.M. The metal ion M is likely:
A) Cr2+ 2+ 2+
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Answer: B (3.87 B.M corresponds to 3 unpaired electrons. Co2+ is d7 , which is high spin t2g 5 eg 2 in water).
19. The linkage isomerism is shown by ligands like:
A) en- -
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Answer: B (Ambidentate ligands like SCN- can coordinate via S or N).
20. The CFSE of a d6 low spin octahedral complex is:
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Answer: -2.4 Δo + 3P (All 6 electrons in t2g : 6 × -0.4 = -2.4).
21. Which complex is kinetically inert?
A) [Ni(H2 O)6 ]2+ 2 O)6 ]3+ 2 O)6 ]2+
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Answer: B (d3 and low spin d6 octahedral complexes are generally kinetically inert).
22. The hapticity (η) of the cyclopentadienyl ligand in Ferrocene is:
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Answer: 5 (All five carbons are equally bonded to the Fe atom).
23. The correct order of Trans-effect is:
A) CN- > NH3 > Cl- - > Cl- > NH3 3 > Cl- > CN-
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Answer: B (Strong π-acceptors have high trans-effect).
24. The geometry of Zeise's salt anion [PtCl3 (η2 -C2 H4 )]- is:
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Answer: Square Planar (Coordination around Pt).
25. Hydrate isomerism is exhibited by the formula CrCl3 .6H2 O. How many total hydrate isomers are possible?
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Answer: 3 ([Cr(H2 O)6 ]Cl3 , [Cr(H2 O)5 Cl]Cl2 .H2 O, and [Cr(H2 O)4 Cl2 ]Cl.2H2 O).
26. Which of the following is an example of an "Inverse Spinel"?
A) MgAl2 O4 2 O4 3 O4 (Magnetite)
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Answer: C (Fe3+ has a higher CFSE in tetrahedral sites or CFSE of Fe2+ is higher in octahedral sites compared to Fe3+ ).
27. The number of d-d transitions observed in the electronic spectrum of [Ti(H2 O)6 ]3+ is one, but the peak is broad and asymmetric due to:
A) Spin-orbit coupling
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Answer: B (The excited state eg 1 undergoes distortion, splitting the transition).
28. The coordination number of Cerium in [Ce(NO3 )6 ]2- is:
A) 6
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Answer: B (Nitrate acts as a bidentate ligand towards lanthanides).
29. Which complex has the shortest Metal-Carbon bond length?
A) [V(CO)6 ]- 6 ]6 ]+
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Answer: A (Highest back-bonding due to negative charge on metal increases M-C bond order).
30. The spin-only magnetic moment of [Ni(H2 O)6 ]2+ is 2.83 BM. The value of μeff is often slightly higher (~3.2 BM) due to:
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Answer: Orbital contribution (mixing of the T ground state with higher states).
31. Among the following, the most stable complex is:
A) [Fe(H2 O)6 ]3+ 2 O4 )3 ]3- 6 ]3-
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Answer: B (Chelate effect of the oxalate ligand).
32. The number of unpaired electrons in a tetrahedral d7 complex is:
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Answer: 3 (Config: e4 t2 3 ). Tetrahedral complexes are almost always high-spin.
33. The "Hole Formalism" suggests that a d1 octahedral system is electronically analogous to:
A) d9 octahedral4 octahedral6 octahedral
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Answer: A (A d9 system can be treated as a d10 system with one "hole").
34. Which of the following is a "non-innocent" ligand?
A) NO (Nitrosyl)3 2 O
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Answer: A (NO can exist as NO+ , NO- , or neutral NO, making oxidation state assignment difficult).
35. The CFSE of a high-spin d7 octahedral complex is:
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Answer: -0.8 Δo (Config: t2g 5 eg 2 . Calculation: 5 × -0.4 + 2 × 0.6 = -0.8).
36. What is the correct order of the nephauxetic effect (cloud expanding) for the following ligands?
A) F- < H2 O < I- - < H2 O < F- 2 O < F- < I-
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Answer: A (Covalency increases from F- to I- , increasing the nephauxetic effect).
37. The total number of ions produced by [Co(NH3 )4 Cl2 ]Cl in water is:
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Answer: 2 (One [Co(NH3 )4 Cl2 ]+ cation and one Cl- anion).
38. In the reaction of [PtCl4 ]2- with NH3 , the final product formed is:
A) cis-[PtCl2 (NH3 )2 ]2 (NH3 )2 ]
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Answer: A (Based on the Trans-effect: Cl- has a higher trans-directing power than NH3 ).
39. The geometry of [Cu(NH3 )4 ]2+ is:
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Answer: Square Planar (d9 system with strong field ligands usually undergoes dsp2 hybridization).
40. The number of microstates for a d2 configuration is:
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Answer: 45 (Calculation: 10! / (2! × 8!)).
41. The Effective Atomic Number (EAN) of Central Metal in [Fe(CN)6 ]4- is:
A) 34
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Answer: C (Fe2+ has 24 electrons. 24 + (6 × 2) = 36. It follows the 18-electron rule/Krypton config).
42. For Lanthanide ions, the magnetic moment is calculated using the formula μ = g√[J(J+1)]. This is because:
A) Spin-only formula is sufficient
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Answer: C (4f electrons are deeply buried and orbital momentum is not quenched by ligands).
43. Which of the following is the most likely geometry for [Ni(CO)4 ]?
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Answer: Tetrahedral (Ni is in 0 oxidation state, d10 configuration, sp3 hybridization).
44. In the Molecular Orbital (MO) diagram of an octahedral complex, the π-acceptor ligands:
A) Increase Δo o o
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Answer: A (Pi-acceptance stabilizes the t2g level, increasing the gap between t2g and eg *).
45. The number of possible optical isomers for [Co(en)3 ]3+ is:
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Answer: 2 (A pair of enantiomers: Δ and Λ forms).
46. Which of the following statements about the 'Nephelauxetic Series' is correct?
A) It ranks ligands by their ability to increase d-electron cloud expansion.
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Answer: A (As covalency increases, electrons spread out/expand, reducing electron-electron repulsion).
47. The geometry of [PtCl4 ]2- is square planar, but [NiCl4 ]2- is tetrahedral. This difference is primarily due to:
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Answer: The higher Δo of 5d metals (Pt). 5d metals always form square planar complexes with d8 configurations regardless of ligand strength.
48. Identify the number of M-M bonds in [Mn2 (CO)10 ]:
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Answer: 1 (Each Mn needs 1 more electron to satisfy the 18-electron rule).
49. The IUPAC name for [Co(NH3 )5 (CO3 )]Cl is:
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Answer: Pentaamminecarbonatocobalt(III) chloride.
50. Which electronic transition is responsible for the yellow color of [CdS]?
A) d-d transition
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Answer: B (Ligand-to-Metal Charge Transfer from S2- to Cd2+ ).
