Coordination Compounds — Advanced Notes & 50 MCQs

1. A ligand is defined as:

1. A central metal ion
2. A molecule or ion that donates electrons to a metal center ✅
3. A spectator ion only
4. A solvent molecule only

2. Which ligand is bidentate?

1. Cl-
2. en (ethylenediamine) ✅
3. NH3
4. H2O

3. Coordination number is best described as:

1. Number of unpaired electrons
2. Number of ligand donor atoms directly bonded to the metal ✅
3. Oxidation state of metal
4. Charge on complex

4. Which geometry is typical for coordination number 6?

1. Tetrahedral
2. Octahedral ✅
3. Linear
4. Square planar

5. According to Crystal Field Theory, in an octahedral complex d-orbitals split into:

1. eg (lower) and t2g (higher)
2. t2g (lower) and eg (higher) ✅
3. p and s orbitals
4. No splitting

6. Which ligand is a strong field ligand (causes large Δo)?

1. Br-
2. CN- ✅
3. I-
4. Cl-

7. Which complex shows geometrical isomerism?

1. [Co(NH3)6]3+
2. [Pt(NH3)2Cl2] (cis/trans) ✅
3. [Fe(CN)6]4-
4. [Ni(CO)4]

8. Chelation effect refers to:

1. Reduction in complex stability when polydentate ligands bind
2. Enhanced stability of complexes formed by multidentate ligands ✅
3. Only color change
4. Decrease in coordination number

9. The IUPAC name of [Fe(H2O)6]2+ is:

1. Hexaaquairon(III)
2. Hexaaquairon(II) ✅
3. Iron hexaaqua(II)
4. Iron(OH)6 2+

10. Which complex is diamagnetic (no unpaired electrons)?

1. [Cu(H2O)6]2+
2. [Ni(CN)4]2- (square planar d8, low-spin) ✅
3. [Fe(H2O)6]2+
4. [Mn(H2O)6]2+

11. Stepwise formation constant (K1, K2...) relates to:

1. Successive addition of ligands to the metal center ✅
2. Only overall stability
3. Only precipitation reactions
4. None of the above

12. Which complex ion is called ferrocyanide?

1. [Fe(CN)6]3-
2. [Fe(CN)6]4- ✅
3. [Fe(CN)5]2-
4. None of the above

13. Which is an ambidentate ligand?

1. en (binds through two N atoms)
2. NO2- (can bind through N or O) ✅
3. NH3 (monodentate)
4. Cl- (monodentate)

14. Which of the following shows optical isomerism?

1. [Co(NH3)6]3+
2. [Co(en)3]3+ ✅
3. [Pt(NH3)4]2+
4. [Fe(CN)6]4-

15. The spectrochemical series arranges ligands according to:

1. Their boiling points
2. Their ability to split d-orbital energies (field strength) ✅
3. Only their denticity
4. None of the above

16. Which theory explains the color and magnetism of many complexes by d-orbital splitting?

1. VSEPR
2. Crystal Field Theory (CFT) ✅
3. Valence Bond Theory (only bonding picture)
4. Ideal gas theory

17. Which complex is called 'hexaaquacopper(II)'?

1. [Cu(NH3)6]2+
2. [Cu(H2O)6]2+ ✅
3. [Cu(CN)6]4-
4. [CuCl4]2-

18. Which complex is an example of a coordination compound used in medicine?

1. [Fe(CN)6]4-
2. Cisplatin (Pt(NH3)2Cl2) used in chemotherapy ✅
3. [Ni(CO)4]
4. [Ag(NH3)2]+ only

19. Which is the correct name for [CoCl(NH3)5]2+?

1. Pentaamminechlorocobalt(III) ✅
2. Chloroamminecobalt(II)
3. Pentaamminechlorocobalt(II)
4. Hexaamminecobalt(III)

20. Which of the following increases stability of complexes?

1. Monodentate ligands only
2. Chelating (multidentate) ligands ✅
3. Large counter-ions always
4. Lower temperature only

21. A complex showing linkage isomerism is due to:

1. Different geometrical positions
2. Ligand attaching through different donor atoms (e.g., NO2- binding through N or O) ✅
3. Change in oxidation state only
4. Only different counter-ions

22. Which of the following complexes is square planar?

1. [Ni(CO)4] (tetrahedral)
2. [PtCl4]2- ✅
3. [Fe(CN)6]4-
4. [Co(NH3)6]3+

23. Which ligand would produce the smallest octahedral splitting energy (Δo)?

1. CN- (strong field)
2. I- (weak field) ✅
3. NO2-
4. CO

24. Which complex is called 'hexacyanoferrate(II)'?

1. [Fe(CN)6]3-
2. [Fe(CN)6]4- ✅
3. [Fe(CN)5]3-
4. [Fe(CN)6]2-

25. Which factor does NOT affect the stability constant of a complex?

1. Nature of metal ion
2. Nature of ligand
3. Color of the ligand (irrelevant) ✅
4. Solvent and temperature

26. Which complex ion is used in qualitative analysis to detect iron?

1. Prussian blue forms with ferric ion and ferrocyanide ✅
2. Methylene blue only
3. None of the above
4. Silver chloride precipitation

27. Which complex shows linkage isomerism as an example?

1. [Co(NH3)6]3+
2. [Co(NH3)5(NO2)]2+ (NO2-/ONO-) ✅
3. [Pt(NH3)2Cl2]
4. [Fe(CN)6]4-

28. Which experimental method helps determine the number of unpaired electrons in a complex?

1. IR spectroscopy only
2. Magnetic susceptibility measurements ✅
3. pH titration only
4. Boiling point elevation

29. Which complex is used as an antidote to mercury poisoning historically?

1. EDTA only
2. Dimercaprol (a chelating agent) ✅
3. NaCl solution
4. CuSO4

30. Which of the following is correct about ambidentate ligands?

1. They bind through multiple donor atoms simultaneously
2. They can bind through either of two different atoms (but typically one at a time) ✅
3. They are always polydentate
4. They never form isomers

31. Which complex is commonly used as an oxidizing agent in analytical chemistry?

1. Potassium ferrocyanide
2. Potassium dichromate and permanganate are common — KMnO4 often used ✅
3. Sodium chloride
4. Ammonium nitrate

32. What is the Oxidation state of Co in [Co(NH3)6]3+?

1. +2
2. +3 ✅
3. 0
4. -1

33. Which of the following does NOT act as a ligand?

1. NH3
2. H2O
3. Ne (noble gas inert) ✅
4. Cl-

34. Which complex ion is formed in the reaction of Cu2+ with excess NH3?

1. [Cu(NH3)4(H2O)2]2+ (tetraamminecopper(II)) ✅
2. [Cu(NH3)2]+ only
3. [Cu(NH3)6]4+
4. Cu(NH3)2 solid

35. Which complex would you expect to be low-spin?

1. Fe2+ with weak-field ligands
2. Fe2+ with CN- (strong-field) — likely low-spin ✅
3. Mn2+ with H2O (usually high-spin)
4. None of the above

36. Which ligand is neutral but donates an electron pair to metal?

1. Cl- (anionic)
2. NH3 (neutral donor) ✅
3. CN- (anionic)
4. CO3 2- (anionic)

37. Which of the following complexes shows linkage isomerism with ligand SCN-?

1. [Fe(SCN)6]3-
2. Complexes where SCN- can bind through S or N (e.g., [Co(NH3)5SCN]2+) ✅
3. Only halide complexes
4. None of the above

38. Which method is commonly used to determine stability constants experimentally?

1. Chromatography only
2. Spectrophotometry (monitoring complex formation) ✅
3. Melting point analysis
4. None of the above

39. Which of the following complexes is an example of a metal carbonyl?

1. [Fe(H2O)6]2+
2. Fe(CO)5 (iron pentacarbonyl) ✅
3. [Co(NH3)6]3+
4. [CuCl4]2-

40. Which complex ion is used in EDTA titration for water hardness determination?

1. Ca-EDTA and Mg-EDTA complexes are formed — indicator is Eriochrome Black T ✅
2. Only Fe-EDTA
3. Only Cu-EDTA
4. None of the above

41. Which is the correct formula for aqua ion of chromium(III)?

1. [Cr(H2O)4]2+
2. [Cr(H2O)6]3+ ✅
3. [Cr(H2O)6]2+
4. [Cr(H2O)5]3+

42. Which complex is known for being an example of inert complex (slow ligand substitution)?

1. [Ni(H2O)6]2+
2. [Cr(H2O)6]3+ (Cr3+ complexes are often kinetically inert) ✅
3. [Fe(H2O)6]2+
4. [Cu(H2O)6]2+

43. Which of the following is a chelating agent used in medicine and industry?

1. NaCl
2. EDTA ✅
3. HCl
4. O2

44. Which complex demonstrates linkage isomerism where nitrite binds through O instead of N?

1. [PtCl4]2-
2. [Co(NH3)5(NO2)]2+ / [Co(NH3)5(ONO)]2+ ✅
3. [Fe(CN)6]4-
4. None of the above

45. Which of the following promotes the formation of low-spin octahedral complexes?

1. Weak-field ligand and small Δo
2. Strong-field ligand and large Δo ✅
3. High temperature always
4. Large ionic radius only

46. Which of the following is TRUE about metal carbonyls?

1. CO is a weak field ligand only
2. CO is a strong field ligand and forms back-bonding with metals ✅
3. They are always ionic
4. They never act as catalysts

47. Which metal in haem carries oxygen in blood?

1. Copper
2. Iron (Fe in heme/hemoglobin) ✅
3. Calcium
4. Zinc

48. Which of the following is true about the chelate effect?

1. Only enthalpy change matters
2. Entropy increase on formation contributes significantly to chelate stability ✅
3. Chelates are always less stable
4. Number of donor atoms is irrelevant

49. Which complex would show Jahn–Teller distortion commonly?

1. d10 octahedral complexes
2. d9 octahedral complexes like Cu2+ (distort due to degeneracy) ✅
3. d0 complexes
4. All d5 high-spin complexes only