9. Coordination compounds 12th Chem CET MCQs
[2015] 1. [Cr(NH3)6][Cr(SCN)6] and [Cr(NH3)2(SCN)4][Cr(NH3)4(SCN)2] are examples of what type of isomerism?
Correct Answer: (C) Coordination isomerism
Solution: Coordination isomerism occurs when there is an interchange of ligands between the cationic and anionic coordination spheres of different metal ions.
[2016] 2. Which of the following is a neutral complex?
Correct Answer: (A) [Pt(NH3)2Cl2]
Solution: A neutral complex has no net charge. In [Pt(NH3)2Cl2], the +2 charge of Pt is balanced by two -1 charges of Cl atoms inside the coordination sphere.
[2017] 3. Which of the following coordinate complexes is an exception to EAN rule? (At. No. Pt=78, Fe=26, Zn=30, Cu=29)
Correct Answer: (D) [Cu(NH3)4]2+
Solution: EAN = Z - (O.S) + 2(C.N). For Cu complex: 29 - 2 + 2(4) = 35. Since 35 is not a noble gas atomic number (Kr=36), it is an exception.
[2017] 4. The CORRECT charge on and coordination number of 'Fe' in K3[Fe(CN)6] are respectively:
Correct Answer: (B) +3, 6
Solution: In K3[Fe(CN)6], 3(+1) + x + 6(-1) = 0, giving x = +3. There are 6 CN ligands, so C.N. is 6.
[2018] 5. What is the oxidation number of gold in the complex [AuCl4]-?
Correct Answer: (B) +3
Solution: Let oxidation state be x. x + 4(-1) = -1 → x - 4 = -1 → x = +3.
[2020] 6. Which ligand among the following has the highest splitting power of d-orbitals?
Correct Answer: (C) CO
Solution: According to the Spectrochemical series, CO is a very strong field ligand and causes maximum splitting of d-orbitals.
[2019] 7. Which among the following is an example of ionization isomer?
Correct Answer: (A)
Solution: Ionization isomers give different ions in solution. Option A gives Br- in one case and SO42- in the other.
[2019] 8. Which dispositive ion of following metals form most stable coordinate complex with ammonia?
Correct Answer: (C) Cu (Z=29)
Solution: Stability of divalent metal complexes follows the Irving-Williams series: Mn < Fe < Co < Ni < Cu > Zn. Cu2+ is the most stable.
[2019] 9. Which among the following is a neutral complex?
Correct Answer: (D) [Pt(NH3)2Cl2]
Solution: Cisplatin [Pt(NH3)2Cl2] is a neutral molecule with no ionizable counter-ions outside the brackets.
[2019] 10. The effective atomic number of Iron (Z=26) in [Fe(CN)6]3- is:
Correct Answer: (A) 35
Solution: Fe in [Fe(CN)6]3- is in +3 state. EAN = 26 - 3 + (6 × 2) = 23 + 12 = 35.
[2020] 11. Identify the oxidation state of Cr in K3[Cr(C2O4)3].
Correct Answer: (B) +3
Solution: In K3[Cr(C2O4)3], 3(+1) + x + 3(-2) = 0[cite: 127]. This simplifies to 3 + x - 6 = 0, giving x = +3[cite: 132].
[2020] 12. Which among the following complexes is heteroleptic and cationic in nature?
Correct Answer: (A) [Co(NH3)4Cl2]Cl
Solution: A heteroleptic complex has more than one type of ligand[cite: 143]. Option A contains both NH3 and Cl ligands, and the coordination sphere [Co(NH3)4Cl2]+ is cationic[cite: 144].
[2020] 13. Which statement from following is TRUE for a complex hexamminecobalt(III) chloride?
Correct Answer: (A) In this oxidation state of cobalt is +3.
Solution: Hexamminecobalt(III) chloride is [Co(NH3)6]Cl3. The Roman numeral (III) directly indicates the oxidation state of Cobalt is +3[cite: 148, 150].
[2020] 14. Which among the following coordination compounds does not have coordination number equal to number of ligands?
Correct Answer: (C) [Co(en)3]3+
Solution: 'en' (ethylenediamine) is a bidentate ligand[cite: 165, 170]. Therefore, 3 'en' ligands provide 6 donor atoms, making the coordination number 6, which is not equal to the number of ligands (3).
[2020] 15. What is the type of hybridization and the geometry respectively found in [CoF6]3-?
Correct Answer: (A) sp3d2 and octahedral
Solution: Co3+ with weak field F- ligands forms a high-spin outer orbital complex using sp3d2 hybridization, resulting in an octahedral geometry[cite: 174, 176].
[2020] 16. What is the oxidation state and coordination number of platinum respectively in [Pt(NH3)6]4+?
Correct Answer: (D) +4 and 6
Solution: NH3 is neutral, so the charge on Pt equals the complex charge (+4)[cite: 77, 81]. There are 6 ammine ligands, so the coordination number is 6.
[2020] 17. Identify the coordinate complex having ambidentate ligand from following.
Correct Answer: (C) Sodiumhexanitrito-N-cobaltate(III)
Solution: The nitrito (NO2-) ligand is ambidentate as it can coordinate through either Nitrogen or Oxygen[cite: 82, 83].
[2020] 18. Which statement is correct according to Werner's theory when CoCl3.6NH3 precipitates 3 moles of AgCl?
Correct Answer: (B) 3 Cl atoms are in ionization sphere
Solution: Precipitation of 3 moles of AgCl indicates that 3 Chloride ions are present in the ionizable (outer) sphere[cite: 84, 85, 111].
[2020] 19. What is the oxidation number of central metal atom in [Cr(NH3)6](NO3)3?
Correct Answer: (D) +3
Solution: NH3 is neutral and NO3 has a -1 charge[cite: 129, 136]. Therefore, x + 6(0) + 3(-1) = 0, giving x = +3[cite: 142].
[2020] 20. What is systematic name of [Co(NH3)4Cl2]Cl?
Correct Answer: (B) Tetramninedichlorocobalt(III) chloride
Solution: Following IUPAC rules: ligands are named alphabetically (ammine before chloro), prefixes indicate quantity, and metal oxidation state is in Roman numerals[cite: 154, 155].
[2020] 21. Which of the following is a property of coordination compound and not of double salt?
Correct Answer: (B)
Solution: Coordination compounds retain their identity in solution and do not show the properties of individual constituent ions, unlike double salts.
[2021] 22. Identify neutral complex from the following.
Correct Answer: (B) [Fe(CO)5]
Solution: Pentacarbonyliron(0) has no charge on the coordination sphere and no counter-ions, making it a neutral complex.
[2021] 23. Identify the magnetic behavior and structure of [Ni(CN)4]2- complex from the following.
Correct Answer: (C) Diamagnetic and square planar
Solution: CN- is a strong field ligand causing pairing of electrons in Ni2+ (d8). This leads to dsp2 hybridization, which is square planar and diamagnetic.
[2021] 24. Identify cationic complex from following.
Correct Answer: (D) [PtBr2(NH3)4]Br2
Solution: This complex dissociates into [PtBr2(NH3)4]2+ and 2Br-. Since the complex sphere carries a positive charge, it is cationic.
[2021] 25. What type of hybridization is present in Ni of [Ni(Cl)4]2- and [Ni(CN)4]2- respectively?
Correct Answer: (B) sp3 and dsp2
Solution: Cl- is a weak field ligand (no pairing, sp3 tetrahedral), while CN- is a strong field ligand (pairing occurs, dsp2 square planar).
[2021] 26. What is IUPAC name of [Co(H2O)(NH3)5]I3?
Correct Answer: (A) Pentaammineaquacobalt(III) iodide
Solution: Ligands are named alphabetically (ammine, then aqua). Co is in +3 state, and the counter ion is iodide.
[2022] 27. Identify CORRECT pair of properties of [Co(NH3)6]3+ complex ion.
Correct Answer: (A) Low spin, diamagnetic
Solution: NH3 is a strong field ligand for Co3+, causing pairing of all d-electrons (d6 configuration), making it low-spin and diamagnetic.
[2022] 28. Identify anionic complex from following.
Correct Answer: (D) Sodium hexanitrocobaltate(III)
Solution: The name ends in "-ate", indicating the complex part [Co(NO2)6]3- carries a negative charge.
[2022] 29. Which among the following cations forms the least stable complex if the ligand is same?
Correct Answer: (C) Cd2+
Solution: Cd2+ has a larger ionic radius compared to the first-row transition metals, leading to lower charge density and a less stable complex.
[2022] 30. Identify the use of EDTA from following.
Correct Answer: (D) Treatment of lead poisoning.
Solution: EDTA is a chelating agent used in medicinal chemistry to remove toxic heavy metals like lead from the body.
[2022] 31. What type of isomerism is exhibited by [Co(NH3)6][Cr(CN)6] and [Cr(NH3)6][Co(CN)6]?
Correct Answer: (C) Coordination isomerism
Solution: Coordination isomerism occurs when ligands are interchanged between the cationic and anionic coordination spheres of different metal ions.
[2022] 32. How many unpaired electrons are present in cobalt ion in +3 oxidation state prior to hybridization in [CoF6]3- complex ion?
Correct Answer: (B) 4
Solution: Co3+ has a 3d6 configuration. Since F- is a weak field ligand, no pairing occurs, resulting in 4 unpaired electrons in the t2g and eg orbitals.
[2022] 33. If four different coordinate compounds A, B, C and D have EAN 18, 36, 54 and 35 respectively, identify the compound that does not obey EAN rule.
Correct Answer: (B) D
Solution: The EAN rule is followed when the effective atomic number equals the atomic number of a noble gas (18, 36, or 54). Compound D (35) is the exception.
[2022] 34. Which element from following forms a complex that is used as medicine for treatment of cancer?
Correct Answer: (C) Pt
Solution: Platinum forms Cisplatin [Pt(NH3)2Cl2], which is a prominent anti-cancer drug.
[2022] 35. Identify monodentate ligand from following.
Correct Answer: (C) and (D)
Solution: Both Cyanide and Thiocyanate are monodentate (specifically ambidentate) because they bond through only one donor atom at any given time.
[2022] 36. Identify cationic complex from following.
Correct Answer: (C) Pentaamminechlorocobalt(III) sulphate
Solution: This compound contains the complex cation [Co(NH3)5Cl]2+ paired with the sulphate anion.
[2022] 37. Which among the following complexes does NOT exhibit different geometrical isomers?
Correct Answer: (A) [MA6]
Solution: Octahedral complexes with six identical ligands [MA6] cannot form geometrical isomers because all positions are equivalent.
[2022] 38. Identify the formula of Bis(ethylenediamine)dithiocyanatoplatinum(IV).
Correct Answer: (A) [Pt(en)2(SCN)2]2+
Solution: Platinum (IV) means +4 charge. 'en' is neutral. SCN is -1. Sum = +4 + 0 + 2(-1) = +2. Therefore, the complex ion is [Pt(en)2(SCN)2]2+.
[2022] 39. Which among the following cations forms a most stable complex with the same ligand?
Correct Answer: (A) Co2+
Solution: Following the Irving-Williams series (Mn < Fe < Co < Ni < Cu), Cobalt(II) forms more stable complexes than Iron(II) or Manganese(II).
[2022] 40. What is the oxidation state of cobalt in a complex [Co(NH3)6]3+?
Correct Answer: (B) 3+
Solution: NH3 is a neutral ligand (charge = 0). Thus, the charge on the complex (+3) is solely due to the oxidation state of the central Cobalt ion.
[2022] 41. Identify the type of block element from following that contains the metallic element forming Haemoglobin complex.
Correct Answer: (D) d-block
Solution: Haemoglobin is a coordination compound of Iron (Fe). Iron is a transition element belonging to the d-block of the periodic table.
[2022] 42. Which element from following is present in cisplatin complex?
Correct Answer: (D) Pt
Solution: Cisplatin has the chemical formula [Pt(NH3)2Cl2]. The central metallic element is Platinum (Pt).
[2022] 43. Which among the following complexes exhibits the geometrical as well as optical isomerism?
Correct Answer: (B) [PtCl2(en)2]2+
Solution: This complex of type [M(AA)2X2] exists as cis and trans isomers (geometrical). The cis-isomer is non-superimposable on its mirror image, thus showing optical isomerism.
[2023] 44. What is the value of number of electrons donated by ligand molecules in a complex [Fe(CN)6]3- if EAN is 35 and Fe(Z=26)?
Correct Answer: (D) 12
Solution: Coordination number is 6. Each ligand (CN-) is monodentate and donates one pair of electrons. Total electrons donated = 6 × 2 = 12.
[2022] 45. Identify the co-ordination number of cobalt ion in hexaamminecobalt(III) iodide complex.
Correct Answer: (B) 6
Solution: Hexaammine means there are 6 ammine (NH3) ligands attached to the central cobalt ion. Thus, the coordination number is 6.
[2022] 46. Which of the following statements is true about complex ions [Ni(Cl)4]2- and [Ni(CN)4]2-?
Correct Answer: (D)
Solution: Cl- is a weak field ligand (no pairing, paramagnetic), while CN- is a strong field ligand (pairing occurs, diamagnetic).
[2023] 47. Identify monodentate ligand from the following.
Correct Answer: (A) Cyanide ion
Solution: Cyanide (CN-) coordinates through a single donor atom. Ethylenediamine and Oxalate are bidentate, while EDTA is hexadentate.
[2023] 48. Which from the following coordinate complexes contains anionic and neutral ligands in it?
Correct Answer: (D) [Co(H2O)(NH3)5]I3
Solution: Option D contains H2O (neutral) and NH3 (neutral). *Correction based on PDF options:* If the question implies mixed types, look for complexes like [Co(NH3)4Cl2]Cl (Question 11 logic). However, per the provided list for Q48, D is the heteroleptic choice.
[2023] 49. What is coordination number of central metal ion in [Fe(C2O4)3]3-?
Correct Answer: (D) 6
Solution: Oxalate (C2O42-) is a bidentate ligand. There are 3 oxalate ligands, so total donor atoms = 3 × 2 = 6.
[2023] 50. Which from following formulae is of sodium hexanitrocobaltate(III)?
Correct Answer: (A) Na3[Co(NO2)6]
Solution: Sodium is Na+, hexanitro is (NO2)6, and Cobalt(III) is Co3+. Charge balance: 3(+1) + (+3) + 6(-1) = 0.
[2023] 51. What is the number of moles of donor atoms in n mole of NO2?
Correct Answer: (D) n
Solution: NO2 (Nitro/Nitrito) is a monodentate ligand. This means each molecule of NO2 has only 1 donor atom coordinating at a time. Therefore, n moles of ligand contain n moles of donor atoms.
[2023] 52. What type of ligand the EDTA is?
Correct Answer: (D) Hexadentate
Solution: EDTA (Ethylenediaminetetraacetate) has two nitrogen donor atoms and four oxygen donor atoms (from carboxylate groups), allowing it to bind to a metal ion at six different points.
[2023] 53. Identify neutral complex from following.
Correct Answer: (A) Triamminetrithiocyanatorhodium(III)
Solution: In [Rh(NH3)3(SCN)3], the +3 charge of Rh is balanced by three -1 charges of SCN ligands, and there are no ions outside the sphere. Options C and D are ions, and B is a salt.
[2023] 54. What is the number of unpaired electrons present in nickel ion of [NiCl4]2- complex?
Correct Answer: (C) 2
Solution: Ni2+ has a 3d8 configuration. Cl- is a weak field ligand and does not cause pairing. Following Hund's rule, there are 2 unpaired electrons in the 3d orbitals.
[2022] 55. Which from following is a neutral ligand?
Correct Answer: (A) Aqua
Solution: Aqua refers to the water molecule (H2O), which carries no electrical charge. Sulphato (SO42-), Carbonato (CO32-), and Bromo (Br-) are all anionic ligands.
[2023] 56. Which from following complexes contains only anionic ligands?
Correct Answer: (B) Potassium trioxalatoaluminate (III)
Solution: In [Al(C2O4)3]3-, the only ligand is oxalate (C2O42-), which is an anionic ligand. The other options contain neutral ligands like ammine (NH3) or aqua (H2O).
[2023] 57. Identify number of moles of donor atoms in 2n mole of SCN.
Correct Answer: (D) 2n
Solution: SCN (Thiocyanate) is a monodentate ligand (it uses only 1 donor atom at a time, either S or N). Therefore, the number of moles of donor atoms is equal to the number of moles of the ligand itself.
[2023] 58. Identify neutral ligand from following.
Correct Answer: (A) Ammine
Solution: Ammine refers to the ammonia molecule (NH3), which is a neutral molecule. Nitrato (NO3-), Cyano (CN-), and Chloro (Cl-) are all anions.
[2023] 59. Identify heteroleptic complex from following.
Correct Answer: (A) Tetraamminediaquacobalt (III) chloride
Solution: A heteroleptic complex contains more than one type of ligand. Option A has both ammine (NH3) and aqua (H2O) ligands. The other options contain only one type of ligand.
[2023] 60. Which from following complexes is heteroleptic?
Correct Answer: (C) Pentaamminecarbonatocobalt (III) chloride
Solution: This complex contains two different types of ligands in the coordination sphere: ammine (NH3) and carbonato (CO32-).
[2023] 61. Identify the formula of potassium trioxalatoaluminate(III).
Correct Answer: (A) K3[Al(C2O4)3]
Solution: Aluminum is in the +3 oxidation state, and each oxalate (C2O4) has a -2 charge. Total charge of the complex ion is [+3 + 3(-2)] = -3. To balance this, 3 Potassium ions (K+) are required.
[2023] 62. Identify anionic complex from following.
Correct Answer: (C) Tetracyanonickelate(II) ion
Solution: An anionic complex is one where the coordination sphere carries a negative charge. Tetracyanonickelate(II) is [Ni(CN)4]2-. Options A and B are cationic complexes, and D is a neutral complex.
[2023] 63. Identify cationic sphere complex from following.
Correct Answer: (A) Tetraaminecopper(II) ion
Solution: In [Cu(NH3)4]2+, the complex coordination sphere carries a positive charge, making it a cationic sphere complex.
[2023] 64. Which from following formulae is of trioxalatocobaltate(III) ion?
Correct Answer: (D) [Co(C2O4)3]3-
Solution: Cobalt is +3 and three oxalates are 3 × (-2) = -6. The net charge is +3 - 6 = -3. Thus, the formula is [Co(C2O4)3]3-.
[2023] 65. Identify homoleptic complex from following.
Correct Answer: (A) [Co(NH3)6]3+
Solution: A homoleptic complex contains only one type of ligand in its coordination sphere. Here, only NH3 ligands are present. The other options have mixed ligands (heteroleptic).
[2023] 66. Which from following species is NOT a monodentate ligand?
Correct Answer: (B) H2N(CH2)2NH2
Solution: Ethylenediamine (en) is a bidentate ligand because it has two nitrogen atoms that can donate electron pairs simultaneously to the metal. CN, OH, and Cl are all monodentate.
[2023] 67. Identify anionic sphere complex from following.
Correct Answer: (B) Potassium hexacyanoferrate(II)
Solution: In K4[Fe(CN)6], the coordination sphere [Fe(CN)6]4- carries a negative charge, making it an anionic sphere complex.
[2023] 68. Which coordination complex from following contains neutral ligand?
Correct Answer: (A) Pentacarbonyl iron(0)
Solution: Carbonyl (CO) is a neutral ligand. In [Fe(CO)5], all ligands are neutral. Oxalate, nitro, and cyano ligands are all anionic.
[2023] 69. What is the number of donor atoms in oxalate ion that form coordinate bond with central metal ion?
Correct Answer: (D) 2
Solution: Oxalate (C2O42-) is a bidentate ligand, meaning it has 2 oxygen atoms that act as donor atoms to form two coordinate bonds with the metal.
[2023] 70. Which from following species acts as a neutral ligand?
Correct Answer: (A) Carbonyl
Solution: Carbonyl (CO) is a neutral molecule. Thiocyanato (SCN-), Oxalato (C2O42-), and Nitro (NO2-) are all anionic ligands.
[2023] 71. How many molecules of ammonia form coordinate bond with central metal ion in cisplatin?
Correct Answer: (C) 2
Solution: Cisplatin has the formula [Pt(NH3)2Cl2]. It contains two ammonia (ammine) molecules and two chlorine (chloro) atoms coordinated to the central Platinum ion.
[2023] 72. Which from following is CORRECT stability order of complexes formed by metal ions in +2 state with same ligand?
Correct Answer: (A) Cu > Ni > Co
Solution: According to the Irving-Williams series, the stability of complexes for divalent metal ions of the first transition series increases from Mn2+ to Cu2+ (Mn < Fe < Co < Ni < Cu).
[2023] 73. Which among the following ligands is neutral?
Correct Answer: (D) Ethylenediamine
Solution: Ethylenediamine (NH2CH2CH2NH2) is a neutral molecule. Nitro (NO2-), Nitrito (ONO-), and Isothiocyanato (NCS-) are all anionic ligands.
[2023] 74. Identify a coordinate complex from the following having bidentate and ambidentate ligand in it.
Correct Answer: (B) [Pt(en)2(SCN)2]++
Solution: In this complex, 'en' (ethylenediamine) is a bidentate ligand, and SCN (thiocyanate) is an ambidentate ligand.
[2023] 75. What is the value of effective atomic number of chromium (Z=24) in a complex [Cr(CO)6]?
Correct Answer: (A) 36
Solution: Chromium in [Cr(CO)6] is in the zero oxidation state. EAN = Z - (O.S.) + 2(C.N.) = 24 - 0 + 2(6) = 24 + 12 = 36.
[2023] 76. What is the number of chlorine atoms that forms coordinate bond with central metal ion in cisplatin?
Correct Answer: (B) 2
Solution: The chemical formula for cisplatin is [Pt(NH3)2Cl2]. There are 2 Chlorine atoms directly coordinated to the Platinum center.
[2023] 77. What is coordination number of central metal ion in [Co(NH3)5Cl]SO4?
Correct Answer: (D) 6
Solution: In the coordination sphere [Co(NH3)5Cl], there are 5 ammine ligands and 1 chloro ligand. Since all are monodentate, the coordination number is 5 + 1 = 6.
[2023] 78. Which from following is a cationic sphere complex?
Correct Answer: (A) Pentaaminechlorocobalt (III) sulphate
Solution: This compound consists of the [Co(NH3)5Cl]2+ cation and the SO42- anion. Since the coordination sphere carries a positive charge, it is cationic.
[2023] 79. Which from following is an anionic ligand?
Correct Answer: (C) Sulphato
Solution: Sulphato (SO42-) is an anion and acts as an anionic ligand. Ammine (NH3), Aqua (H2O), and Ethylenediamine (en) are neutral ligands.
[2024, 2020] 80. How many donor atoms are involved in EDTA?
Correct Answer: (D) 6
Solution: EDTA (Ethylenediaminetetraacetate) is a hexadentate ligand, meaning it has 6 donor atoms (2 Nitrogen and 4 Oxygen) available to form coordinate bonds.
[2024, 2021] 81. Which from following ligands has highest field strength?
Correct Answer: (D) en
Solution: According to the spectrochemical series, ethylenediamine (en) is a stronger field ligand than EDTA, OH-, and S2-. It causes greater splitting of d-orbitals.
[2024] 82. Identify the coordination number of aluminium in potassium trioxalatoaluminate(III).
Correct Answer: (C) 6
Solution: Oxalate (C2O42-) is a bidentate ligand. Since there are 3 oxalate ligands attached to Al, the coordination number is 3 × 2 = 6.
[2024] 83. What is the number of moles of silver iodide obtained when one mole of pentaammineaquacobalt(III) iodide is treated with excess silver nitrate solution?
Correct Answer: (B) 3
Solution: The formula is [Co(NH3)5(H2O)]I3. There are 3 iodide ions in the ionizable (outer) sphere. Treating 1 mole of this complex with excess AgNO3 will precipitate 3 moles of AgI.
[2024] 84. Identify the coordination number of cobalt in triamminetrinitrocobalt(III).
Correct Answer: (C) 6
Solution: The formula is [Co(NH3)3(NO2)3]. There are 3 ammine and 3 nitro ligands, all of which are monodentate. Total coordinate bonds = 3 + 3 = 6.
[2024] 85. Which among the following donor atoms is present in strong field ligand?
Correct Answer: (D) N
Solution: Ligands with Nitrogen (N) or Carbon (C) donor atoms (like NH3, en, CN-) are generally strong field ligands compared to those with O, S, or Halogen donor atoms.
[2024] 86. Which among the following coordinate complexes involves monodentate ligand only?
Correct Answer: (A), (C), and (D)
Solution: Fluoro (F-), Nitro (NO2-), and Ammine (NH3) are all monodentate. Oxalate in option B is bidentate. *Note: Most accurate answer based on homoleptic monodentate choice is A or C.*
[2024] 87. Identify a charge number of a complex and coordination number of a central metal ion respectively of a trioxalatocobaltate(III) ion.
Correct Answer: (D) -3 and 6
Solution: Cobalt is +3 and three oxalates are 3 × (-2) = -6. Net charge = +3 - 6 = -3. Since oxalate is bidentate, C.N. = 3 × 2 = 6.
[2024] 88. Which of the following compounds exhibits zero oxidation state of iron?
Correct Answer: (C) [Fe(CO)5]
Solution: In metal carbonyls like [Fe(CO)5], the central metal atom is always in the zero oxidation state as CO is a neutral ligand.
[2024] 89. What is the value of magnetic moment produced by Ti3+?
Correct Answer: (B) 1.73 BM
Solution: Ti (Z=22) is [Ar] 3d2 4s2. Ti3+ is 3d1 (n=1 unpaired electron). μ = √[n(n+2)] = √[1(3)] = √3 = 1.73 BM.
[2024] 90. What is the number of moles of silver bromide obtained when one mole of tetraamminedibromoplatinum (IV) bromide is treated with excess silver nitrate solution?
Correct Answer: (A) 2
Solution: The formula is [Pt(NH3)4Br2]Br2. There are 2 bromide ions in the ionizable sphere. Treating 1 mole with excess AgNO3 yields 2 moles of AgBr.
[2024] 91. Find the total number of moles of donor atoms present in one mole trioxalatocobaltate(III) ion.
Correct Answer: (A) 6
Solution: The oxalate ion (C2O42-) is a bidentate ligand, meaning it has 2 donor atoms. For a trioxalato complex, there are 3 ligands, so 3 × 2 = 6 donor atoms.
[2024] 92. Which from following metal ions in their respective oxidation states forms coloured compound?
Correct Answer: (B) Fe2+
Solution: Colour in transition metal compounds is usually due to d-d transitions. Fe2+ (3d6) has unpaired electrons and an incomplete d-subshell. Zn2+, Cu+ (3d10), and Sc3+ (3d0) have either completely filled or empty d-subshells.
[2024] 93. Which from following ligands is able to form linkage isomers?
Correct Answer: (A) SCN
Solution: Linkage isomerism occurs with ambidentate ligands. SCN- can coordinate through Sulfur (thiocyanato) or Nitrogen (isothiocyanato).
[2024] 94. Identify the total number of complexes having bidentate ligands in them from following list: a) Tetracyanonickelate(II) ion, b) Trioxalatocobaltate(III) ion, c) Sodium hexafluoroaluminate(III), d) bis(ethylenediamine)dithiocyanatoplatinum(IV).
Correct Answer: (B) 2
Solution: Complexes (b) and (d) contain bidentate ligands: oxalate in (b) and ethylenediamine (en) in (d). Cyano and fluoro ligands are monodentate.
[2024] 95. What is the number of moles of ionisable Cl- ions in a coordinate complex if it forms two moles of AgCl when treated with silver nitrate solution in excess?
Correct Answer: (B) 2
Solution: The number of moles of AgCl precipitate equals the number of moles of ionisable (outer sphere) Chloride ions. Since 2 moles of AgCl are formed, there are 2 ionisable Cl- ions.
[2024] 96. Which among the following is a correct decreasing order of thermodynamic stability of the complexes?
Correct Answer: (A)
Solution: Stability depends on the nature of the metal (charge and size) and ligand (basic strength/chelating effect). Co3+ complexes are generally very stable due to high charge and small size.
[2024] 97. What is the number of electrons lost by Cr in a complex [Cr(CO)6]?
Correct Answer: (A) 0
Solution: In metal carbonyls like [Cr(CO)6], the metal is in the zero oxidation state. Therefore, it has lost zero electrons.
[2024] 98. Which among the following is a cationic complex?
Correct Answer: (B) [Co(NH3)5Cl]SO4
Solution: This compound dissociates into the complex cation [Co(NH3)5Cl]2+ and the sulphate anion. Options A and D are anionic complexes, and C is neutral.
[2024] 99. What is the EAN of Zn in [Zn(NH3)4]2+?
Correct Answer: (D) 36
Solution: Zn (Z=30), oxidation state is +2, and coordination number is 4. EAN = 30 - 2 + 2(4) = 28 + 8 = 36.
[2024] 100. Which from following ligands is anionic?
Correct Answer: (A) Cyano
Solution: Cyano (CN-) is an anion. Aqua (H2O), Ammine (NH3), and Carbonyl (CO) are all neutral molecules.
[2024] 101. Identify ambidentate ligand from following.
Correct Answer: (A) and (B)
Solution: Both Cyanide and Nitrite are ambidentate. CN- can link via C or N; NO2- can link via N or O. Oxalate and en are bidentate.
[2024] 102. Which from the following statements about [Co(NH3)6]3+ complex is NOT correct?
Correct Answer: (C) It is a high spin complex.
Solution: NH3 acts as a strong field ligand for Co3+, causing pairing of electrons. Thus, it forms a low-spin, diamagnetic complex.
[2024] 103. What is the oxidation state of central metal ion in [Fe(CN)6]4- complex?
Correct Answer: (A) +2
Solution: x + 6(-1) = -4 → x - 6 = -4 → x = +2. Iron is in the +2 oxidation state.
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