Coordination Compounds - MCQs with Explanations

Coordination Compounds - MCQs with Explanations

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Coordination Compounds - MCQs with Explanations

1. The IUPAC name of $Na_{3}[Co(NO_{2})_{6}]$ is

  • (a) sodium cobaltnitrite
  • (b) sodium hexanitrocobaltate(III)
  • (c) sodium hexanitrocobalt(II)
  • (d) sodium hexanitritocobaltate(III).

Correct Answer: (b)

Explanation: The complex is named by stating the cation first, then the number of ligands (hexa-), the ligand name (nitro-), and finally the metal with its oxidation state in Roman numerals (cobaltate(III)) because the complex ion is an anion.

2. The two complexes given below are:

(Refer to structures in source showing two trans-forms of an ethylenediamine complex)

  • (a) geometrical isomers
  • (b) position isomers
  • (c) optical isomers
  • (d) identical.

Correct Answer: (d)

Explanation: Both representations show the same molecule (no isomerism is seen) as they are both trans-forms.

3. Ammonia forms the complex ion $[Cu(NH_{3})_{4}]^{2+}$ with copper ion in the alkaline solution but not in acidic solution. What is the reason for it?

  • (a) In acidic solutions, hydration protects copper ions.
  • (b) In acidic solutions, protons co-ordinate with ammonia molecules forming $NH_{4}^{+}$ ions and $NH_{3}$ molecules are not available.
  • (c) In alkaline solutions, insoluble $Cu(OH)_{2}$ is precipitated which is soluble in excess of any alkali.
  • (d) Copper hydroxide is an amphoteric substance.

Correct Answer: (b)

Explanation: In acidic solutions, the lone pair of electrons on nitrogen in $NH_{3}$ coordinates with $H^{+}$ ions, making them unavailable to coordinate with the copper ion.

4. Among the following complexes, (i) $K_{3}[Fe(CN)_{6}]$, (ii) $[Co(NH_{3})_{6}]Cl_{3}$, (iii) $Na_{3}[Co(ox)_{3}]$, (iv) $[Ni(H_{2}O)_{6}]Cl_{2}$, (v) $K_{2}[Pt(CN)_{4}]$ and (vi) $[Zn(H_{2}O)_{6}](NO_{3})_{2}$ the diamagnetic complexes are:

  • (a) (i), (ii), (iii), (iv)
  • (b) (i), (iii), (v), (vi)
  • (c) (ii), (iii), (v), (vi)
  • (d) (ii), (iii), (iv), (v)

Correct Answer: (c)

Explanation: Complexes (ii), (iii), (v), and (vi) are diamagnetic due to the absence of unpaired electrons, while (i) and (iv) contain unpaired electrons and are paramagnetic.

5. In which of the following coordination entities the magnitude of $\Delta_{o}$ (CFSE in octahedral field) will be maximum (atomic number of $Co=27$)?

  • (a) $[Co(C_{2}O_{4})_{3}]^{3-}$
  • (b) $[Co(H_{2}O)_{6}]^{3+}$
  • (c) $[Co(NH_{3})_{6}]^{3+}$
  • (d) $[Co(CN)_{6}]^{3-}$

Correct Answer: (d)

Explanation: According to the spectrochemical series, $CN^{-}$ is a strong field ligand compared to $NH_{3}, H_{2}O$, and $C_{2}O_{4}^{2-}$, thus producing the maximum splitting parameter ($\Delta_{o}$).

6. Geometrical shapes of the complexes formed by the reaction of $Ni^{2+}$ with $Cl^{-}, CN^{-}$ and $H_{2}O,$ respectively, are:

  • (a) octahedral, tetrahedral and square planar
  • (b) tetrahedral, square planar and octahedral
  • (c) square planar, tetrahedral and octahedral
  • (d) octahedral, square planar and tetrahedral.

Correct Answer: (b)

Explanation: $Ni^{2+}$ with $Cl^{-}$ forms a tetrahedral complex ($sp^{3}$); with $CN^{-}$, a strong field ligand, it pairs electrons to form a square planar complex ($dsp^{2}$); and with $H_{2}O$, it forms an octahedral complex ($sp^{3}d^{2}$).

7. One mole of the complex compound $Co(NH_{3})_{5}Cl_{3},$ gives three moles of ions on dissolution in water. One mole of the same complex reacts with two moles of $AgNO_{3(aq)}$ to yield two moles of $AgCl_{(s)}.$ The structure of the complex is:

  • (a) $[Co(NH_{3})_{5}Cl]Cl_{2}$
  • (b) $[Co(NH_{3})_{3}Cl_{3}]\cdot 2NH_{3}$
  • (c) $[Co(NH_{3})_{4}Cl_{2}]Cl\cdot NH_{3}$
  • (d) $[Co(NH_{3})_{4}Cl]Cl_{2}\cdot NH_{3}$

Correct Answer: (a)

Explanation: The precipitation of 2 moles of $AgCl$ indicates 2 ionisable $Cl^{-}$ ions outside the coordination sphere, while the total number of 3 ions confirms the formula $[Co(NH_{3})_{5}Cl]Cl_{2}$.

8. The stability constants of the complexes formed by a metal ion $(M^{2+})$ with $NH_{3^{\prime}} CN, H_{2}O$ and en are of the order $10^{11}$ $10^{27}$ $10^{15}$, and $10^{8}$ respectively. This shows:

  • (a) en is the strongest ligand
  • (b) $CN^{-}$ is the strongest ligand
  • (c) values cannot predict the strength of the ligand
  • (d) all the ligands are equally strong.

Correct Answer: (b)

Explanation: A higher stability constant indicates a more stable complex and a stronger coordinating ability of the ligand; $CN^{-}$ has the highest value ($10^{27}$).

9. The coordination number and oxidation number of X in the compound $[X(SO_{4})(NH_{3})_{5}]Cl$ will be:

  • (a) 6 and +3
  • (b) 2 and -6
  • (c) 10 and -3
  • (d) 6 and +4

Correct Answer: (a)

Explanation: The coordination number is 6 (five $NH_{3}$ and one $SO_{4}^{2-}$). Given the total charge of the complex is +1 (balanced by $Cl^{-}$), the oxidation state $a$ is found by $a - 2 = +1$, so $a = +3$.

10. How many EDTA molecules are required to make an octahedral complex with $Ca^{2+}$ ion?

  • (a) Six
  • (b) Three
  • (c) One
  • (d) Two

Correct Answer: (c)

Explanation: EDTA is a hexadentate ligand, meaning a single molecule provides all six coordination points necessary for an octahedral geometry.

11. What is the IUPAC name of $Na_{2}[Fe(CN)_{5}NO]$?

  • (a) Pentacyanonitrososodium ferrate(III)
  • (b) Pentacyanonitrososodium ferrate(II)
  • (c) Sodium nitrosoniumpentacyanoferrate(II)
  • (d) Sodium pentacyanonitrosylferrate(III)

Correct Answer: (d)

Explanation: The correct IUPAC nomenclature for sodium nitroprusside is sodium pentacyanonitrosylferrate(III).

12. What is the most likely configuration of the cobalt d-electrons for the species, $[CoCl_{6}]^{3-}$ and $[Co(NO_{2})_{6}]^{3-}?$

  • (a) $[CoCl_{6}]^{3-}$: low spin; $[Co(NO_{2})_{6}]^{3-}$: low spin
  • (b) $[CoCl_{6}]^{3-}$: high spin $;[Co(NO_{2})_{6}]^{3}$: low spin
  • (c) $[CoCl_{6}]^{3-}$: low spin; $[Co(NO_{2})_{6}]^{3-}$: high spin
  • (d) $[CoCl_{6}]^{3-}$: high spin; $[Co(NO_{2})_{6}]^{3-}$: high spin

Correct Answer: (b)

Explanation: Weak field ligands like $Cl^{-}$ lead to high spin complexes, whereas strong field ligands like $NO_{2}^{-}$ produce low spin (spin paired) complexes.

13. Which of the following is considered to be an anti-cancer species?

  • (a) $mer-[Co(NH_{3})Cl_{3}]$
  • (b) $cis-[PtCl_{2}(NH_{3})_{2}]$
  • (c) $cis-K_{2}[PtCl_{2}Br_{2}]$
  • (d) $Na_{2}[CoCl_{4}]$

Correct Answer: (b)

Explanation: The compound $cis$-platin is a well-known chemotherapy drug used to treat various cancers.

14. Which of the following has an optical isomer?

  • (a) $[Co(NH_{3})_{3}Cl]^{+}$
  • (b) $[Co(en)(NH_{3})_{2}]^{2+}$
  • (c) $[Co(H_{2}O)_{4}(en)]^{3+}$
  • (d) $[Co(en)_{2}(NH_{3})_{2}]^{3+}$

Correct Answer: (d)

Explanation: The $cis$-form of $[Co(en)_{2}(NH_{3})_{2}]^{3+}$ lacks a plane of symmetry and is therefore optically active.

15. Coordination number of Cr is six. A complex ion of Cr with $C_{2}O_{4}^{2-}$, en and superoxide ion, $O_{2}^{-}$ has the formula $[Cr(C_{2}O_{4})_{x}(en)_{y}(O_{2})_{z}]^{-}$. The ratio x : y: z will be:

  • (a) 1:1:1
  • (b) 1:1:2
  • (c) 1:2:2
  • (d) 2:1:1

Correct Answer: (b)

Explanation: For a net charge of -1 and a coordination number of 6, the values $x=1, y=1, z=2$ satisfy both conditions ($+3 + 1(-2) + 1(0) + 2(-1) = -1$).

16. A complex $MA_{3}X_{3}$, where A and X are unidentate ligands may give:

  • (a) two geometrical isomers
  • (b) three geometrical isomers
  • (c) two geometrical isomers which can be resolved into a pair of enantiomers
  • (d) two geometrical isomers one of which can be resolved into a pair of enantiomers.

Correct Answer: (a)

Explanation: Complexes of type $MA_{3}X_{3}$ exhibit two geometrical isomers: facial ($fac$-) and meridional ($mer$-).

17. Which of the following statements is incorrect?

  • (a) In $K_{3}[Fe(CN)_{6}],$ the ligand has satisfied only the secondary valency of ferric ion.
  • (b) In $K_{3}[Fe(CN)_{6}],$ the ligand has satisfied both primary and secondary valencies of ferric ion.
  • (c) In $K_{4}[Fe(CN)_{6}],$ the ligand has satisfied both primary and secondary valencies of ferrous ion.
  • (d) In $[Cu(NH_{3})_{4}]SO_{4^{\prime}}$ the ligand has satisfied only the secondary valency of copper.

Correct Answer: (a)

Explanation: In Werner's theory, ligands in the coordination sphere (like $CN^{-}$) satisfy the secondary valency (coordination number), but since they are anions, they also satisfy the primary valency (oxidation state).

18. A complex of a certain metal ion has a magnetic moment of 4.90 BM; another complex of the same metal in the same oxidation state has a zero magnetic moment. The central metal ion could be:

  • (a) $Cr^{III}$
  • (b) $Mn^{II}$
  • (c) $Fe^{III}$
  • (d) $Fe^{II}$

Correct Answer: (d)

Explanation: $Fe^{II}$ ($d^{6}$) can have 4 unpaired electrons (high spin with weak field ligands, $\approx 4.9$ BM) or zero unpaired electrons (low spin with strong field ligands like $CN^{-}$).

19. Which of the following statements is true?

  • (a) If $\Delta_{0}>P,$ strong field ligands and low spin complexes.
  • (b) If $\Delta_{0}
  • (c) If $\Delta_{o}
  • (d) If $f\Delta_{o}>P,$ weak field ligands and low spin complexes.

Correct Answer: (a)

Explanation: When the splitting energy ($\Delta_{o}$) exceeds the pairing energy ($P$), pairing is energetically favorable, leading to low spin complexes.

20. Predict the order of $\Delta_{o}$ for the following compounds: (I) $[Fe(H_{2}O)_{6}]^{2+}$, (II) $[Fe(CN)_{2}(H_{2}O)_{4}]$, (III) $[Fe(CN)_{4}(H_{2}O)_{2}]^{2-}$

  • (a) $\Delta_{o}(I)<\Delta_{o}(II)<\Delta_{o}(III)$
  • (b) $\Delta_{o}(II)<\Delta_{o}(I)<\Delta_{o}(III)$
  • (c) $\Delta_{o}(III)<\Delta_{o}(II)<\Delta_{o}(I)$
  • (d) $\Delta_{o}(II)<\Delta_{o}(III)<\Delta_{o}(I)$

Correct Answer: (a)

Explanation: Since $CN^{-}$ is a stronger field ligand than $H_{2}O,$ the splitting increases with the number of cyanide ions in the complex.

21. Match List I with List II (Species with Geometry/Magnetic Moment)

  • P. $[Ag(CN)_{2}]^{-}$; Q. $[Cu(CN)_{4}]^{3-}$; R. $[Cu(NH_{3})_{4}]^{2+}$; S. $[Fe(CN)_{6}]^{4-}$
  • 1. Square planar and 1.73 BM; 2. Linear and zero; 3. Octahedral and zero; 4. Tetrahedral and zero

Correct Answer: (b)

Explanation: $[Ag(CN)_{2}]^{-}$ is linear and zero (P-2); $[Cu(CN)_{4}]^{3-}$ is tetrahedral and zero (Q-4); $[Cu(NH_{3})_{4}]^{2+}$ is square planar and 1.73 BM (R-1); and $[Fe(CN)_{6}]^{4-}$ is octahedral and zero (S-3).

22. Match the compounds in List I with the oxidation state of cobalt in List II.

  • P. $[Co(NCS)(NH_{3})_{5}]SO_{3}$; Q. $[Co(NH_{3})_{4}Cl_{2}]SO_{4}$; R. $Na_{4}[Co(S_{2}O_{3})_{3}]$; S. $K[Co(CO)_{4}]$
  • 1. +4; 2. -1; 3. +2; 4. +3

Correct Answer: (a)

Explanation: Calculations yield: P is +3 (4); Q is +4 (1); R is +2 (3); and S is -1 (2).

23. Which of the following is most likely structure of $CrCl_{3}.6H_{2}O$ if $1/3$ of total chlorine of the compound is precipitated by adding $AgNO_{3}$ to its aqueous solution?

  • (a) $CrCl_{3}.6H_{2}O$
  • (b) $[Cr(H_{2}O)_{3}Cl_{3}](H_{2}O)_{3}$
  • (c) $[CrCl_{2}(H_{2}O)_{4}]Cl.2H_{2}O$
  • (d) $[CrCl(H_{2}O)_{5}]Cl_{2}.H_{2}O.$

Correct Answer: (c)

Explanation: Precipitating 1/3 of the chlorine (1 out of 3 atoms) means only one $Cl^{-}$ ion is outside the coordination sphere.

24. The correct name of bridged iron carbonyl structure:

  • (a) Tri-$\mu$-carbonylbis(tricarbonyl)iron(0)
  • (b) Hexacarbonyl iron(III)tricarbonylferrate(0)
  • (c) Tricarbonyl iron(0) tricarbonyliron(0) tricarbonyl
  • (d) Nonacarbonyl iron.

Correct Answer: (a)

Explanation: The systematic name for $Fe_{2}(CO)_{9}$ using bridging ligand nomenclature is Tri-$\mu$-carbonylbis(tricarbonyl)iron(0).

25. $Mn^{2+}$ forms a complex with $Br^{-}$ ion. The magnetic moment of the complex is 5.92 BM. The probable formula and geometry of the complex, is:

  • (a) $[MnBr_{4}]^{2-};$ tetrahedral
  • (b) $[MnBr_{4}]^{2-}$; square planar
  • (c) $[MnBr_{6}]^{4-}$; octahedral
  • (d) $[MnBr_{5}]^{3-}$ trigonal planar.

Correct Answer: (a)

Explanation: A magnetic moment of 5.92 BM corresponds to 5 unpaired electrons ($Mn^{2+}$ in $d^{5}$). This configuration and the coordination with $Br^{-}$ suggest $sp^{3}$ hybridisation and tetrahedral geometry.

26. The pair of the compounds in which both the metals are in the highest possible oxidation state is:

  • (a) $[Fe(CN)_{6}]^{3-}$ $[Co(CN)_{6}]^{3-}$
  • (b) $CrO_{2}Cl_{2}, MnO_{4}^{-}$
  • (c) $TiO_{3}, MnO_{2}$
  • (d) $[Co(CN)_{6}]^{3-}, MnO_{3}$.

Correct Answer: (b)

Explanation: In $CrO_{2}Cl_{2}$ (chromyl chloride), Cr is in the +6 state, and in $MnO_{4}^{-},$ Mn is in the +7 state.

27. The value of the 'spin only' magnetic moment for one of the following configurations is 2.84 BM. The correct one is:

  • (a) $d^{4}$ (in strong ligand field)
  • (b) $d^{4}$ (in weak ligand field)
  • (c) $d^{3}$ (in weak as well as in strong fields)
  • (d) $d^{4}$ (in weak field as well as in strong fields)

Correct Answer: (a)

Explanation: A moment of 2.84 BM indicates 2 unpaired electrons. In an octahedral complex with a strong field, a $d^{4}$ configuration results in a low-spin state with 2 unpaired electrons ($t_{2g}^{4} e_{g}^{0}$).

28. Which one of the following has an optical isomer?

  • (a) $[Zn(en)_{2}]^{2+}$
  • (b) $[Zn(en)(NH_{3})_{2}]^{2+}$
  • (c) $[Co(en)_{3}]^{3+}$
  • (d) $[Co(H_{2}O)_{4}(en)]^{3+}$

Correct Answer: (c)

Explanation: $[Co(en)_{3}]^{3+}$ is a chiral octahedral complex that exists as a pair of non-superimposable mirror images (enantiomers).

29. Spin only magnetic moment of the compound $Hg[Co(SCN)_{4}]$ is:

  • (a) $\sqrt{3}$
  • (b) $\sqrt{15}$
  • (c) $\sqrt{24}$
  • (d) $\sqrt{8}$

Correct Answer: (b)

Explanation: Cobalt in this compound is $Co^{2+}$ ($d^{7}$), which has 3 unpaired electrons. The magnetic moment is $\sqrt{3(3+2)} = \sqrt{15}$ BM.

30. The IUPAC name for the complex $[Co(NO_{2})(NH_{3})_{5}]Cl_{2}$ is:

  • (a) nitrito-N-pentaamminecobalt(III) chloride
  • (b) nitrito-N-pentaamminecobalt(II) chloride
  • (c) pentaamminenitrito-N-cobalt(II) chloride
  • (d) pentaamminenitrito-N-cobalt(III) chloride

Correct Answer: (d)

Explanation: The ligands are listed alphabetically (ammine before nitrito), and the oxidation state of Cobalt is +3.

31. The IUPAC name of $K_{2}[Cr(CN)_{2}O_{2}(O)_{2}(NH_{3})]$ is:

  • (a) potassium amminedicyanodioxoperoxochromate (VI)
  • (b) potassium amminecyanoperoxodioxochromate (IV)
  • (c) potassium amminecyanoperoxodioxochromium (VI)
  • (d) potassium amminedicyanoperoxodioxochromyium (IV)

Correct Answer: (a)

Explanation: This name correctly identifies the ligands and the +6 oxidation state of Chromium in the anionic complex.

32. An example for a double salt is:

  • (a) cuprammonium sulphate
  • (b) Mohr's salt
  • (c) potassium ferricyanide
  • (d) cobalthexammine chloride

Correct Answer: (b)

Explanation: Mohr's salt, $(NH_{4})_{2}SO_{4}\cdot FeSO_{4}\cdot 6H_{2}O,$ is a classic example of a double salt that dissociates into simple ions in water.

33. Which of the following complexes does not obey the EAN rule?

  • (a) $[PtCl_{6}]^{2-}$
  • (b) $[Co(NH_{3})_{6}]^{3+}$
  • (c) $[Fe(CN)_{6}]^{3-}$
  • (d) $[Cu(CN)_{4}]^{3-}$

Correct Answer: (c)

Explanation: For $[Fe(CN)_{6}]^{3-},$ the Effective Atomic Number is $26 - 3 + (6 \times 2) = 35,$ which does not match the next noble gas, Krypton (36).

34. Which of the following shall form an octahedral complex?

  • (a) $d^{4}$ (low spin)
  • (b) $d^{8}$ (high spin)
  • (c) $d^{6}$ (low spin)
  • (d) All of these

Correct Answer: (c)

Explanation: In a $d^{6}$ low-spin state, two $d$-orbitals are empty, allowing for $d^{2}sp^{3}$ hybridisation and octahedral geometry.

35. Which of the following will give a pair of enantiomers?

  • (a) $[Pt(NH_{3})_{4}][PtCl_{6}]$
  • (b) $[Co(NH_{3})_{4}Cl_{2}]NO_{2}$
  • (c) $[Cr(NH_{3})_{6}][Co(CN)_{6}]$
  • (d) $[Co(en)_{2}Cl_{2}]Cl$

Correct Answer: (d)

Explanation: The $cis$-isomer of the $[Co(en)_{2}Cl_{2}]^{+}$ ion lacks a plane of symmetry and exists as a pair of enantiomers.

36. Fac-mer isomerism is associated with which one of the following complexes?

  • (a) $[M(AA)_{2}]$
  • (b) $[MA_{3}B_{3}]$
  • (c) $[M(AA)_{3}]$
  • (d) [MABCD]

Correct Answer: (b)

Explanation: Facial ($fac$-) and meridional ($mer$-) isomerism occurs in octahedral complexes with a $3:3$ ratio of different unidentate ligands.

37. A solution containing 0.319 g of $CrCl_{3}\cdot 6H_{2}O$ was passed through a cation exchange resin and required 28.5 mL of 0.125 M NaOH. The correct formula of the complex is:

  • (a) $[Cr(H_{2}O)_{6}]Cl_{3}$
  • (b) $[Cr(H_{2}O)_{5}Cl]Cl_{2}$
  • (c) $[Cr(H_{2}O)_{4}Cl_{2}]Cl$
  • (d) $[Cr(H_{2}O)_{3}Cl_{3}]$

Correct Answer: (a)

Explanation: Based on the molar ratios of the complex and the titrated acid from the exchange resin, 3 moles of $Cl^{-}$ ions are ionisable, confirming the formula $[Cr(H_{2}O)_{6}]Cl_{3}$.

38. Given $Ag^{+} + NH_{3} \rightleftharpoons [Ag(NH_{3})]^{+}$ ($k_{1} = 6.8 \times 10^{-3}$) and $[Ag(NH_{3})]^{+} + NH_{3} \rightleftharpoons [Ag(NH_{3})_{2}]^{+}$ ($k_{2} = 1.6 \times 10^{-3}$), the formation constant of $[Ag(NH_{3})_{2}]^{+}$ is:

  • (a) $1.08 \times 10^{-7}$
  • (b) $1.08 \times 10^{-5}$
  • (c) $1.08 \times 10^{-9}$
  • (d) none of these

Correct Answer: (b)

Explanation: The overall formation constant is the product of the stepwise constants: $K = k_{1} \times k_{2} = 1.08 \times 10^{-5}$.

39. Which one of the following ions forms most stable complex compound?

  • (a) $Cu^{2+}$
  • (b) $Ni^{2+}$
  • (c) $Fe^{2+}$
  • (d) $Mn^{2+}$

Correct Answer: (a)

Explanation: According to the Irving-Williams series, $Cu^{2+}$ typically forms the most stable complexes among these divalent transition metal ions.

40. From the stability constants given, predict which is the strongest ligand? (a) $NH_{3} (K = 4.5 \times 10^{11})$, (b) $CN^{-} (K = 2.0 \times 10^{17})$, (c) $en (K = 3.0 \times 10^{15})$, (d) $H_{2}O (K = 9.5 \times 10^{8})$

  • (a) $NH_{3}$
  • (b) $CN^{-}$
  • (c) $en$
  • (d) $H_{2}O$

Correct Answer: (b)

Explanation: The highest stability constant ($2.0 \times 10^{17}$) indicates that $CN^{-}$ binds most strongly.

41. Which of the following has a square planar geometry?

  • (a) $[PtCl_{4}]^{2-}$
  • (b) $[CoCl_{4}]^{2-}$
  • (c) $[FeCl_{4}]^{2-}$
  • (d) $[NiCl_{4}]^{2-}$

Correct Answer: (a)

Explanation: $Pt^{2+}$ forms a square planar complex ($dsp^{2}$) with $Cl^{-},$ whereas the others listed form tetrahedral complexes with chloride.

42. Which one of the following is an outer orbital complex and exhibits paramagnetic behaviour?

  • (a) $[Ni(NH_{3})_{6}]^{2+}$
  • (b) $[Zn(NH_{3})_{6}]^{2+}$
  • (c) $[Cr(NH_{3})_{6}]^{3+}$
  • (d) $[Co(NH_{3})_{6}]^{3+}$

Correct Answer: (a)

Explanation: $[Ni(NH_{3})_{6}]^{2+}$ uses outer $4d$ orbitals ($sp^{3}d^{2}$) and contains unpaired electrons, making it paramagnetic.

43. Which one has the highest paramagnetism?

  • (a) $Ni(CO)_{4}$
  • (b) $[Co(NH_{3})_{6}]Cl_{3}$
  • (c) $[Ni(NH_{3})_{6}]Cl_{2}$
  • (d) $[Cu(NH_{3})_{4}]Cl_{2}$

Correct Answer: (c)

Explanation: $[Ni(NH_{3})_{6}]^{2+}$ has 2 unpaired electrons, while $[Cu(NH_{3})_{4}]^{2+}$ has only 1. Options (a) and (b) are diamagnetic.

44. Which of the following will give a pair of enantiomorphs?

  • (a) $[Cr(NH_{3})_{6}][Co(CN)_{6}]$
  • (b) $[Co(en)_{2}Cl_{2}]Cl$
  • (c) $[Pt(NH_{3})_{4}][PtCl_{6}]$
  • (d) $[Co(NH_{3})_{4}Cl_{2}]NO_{2}$

Correct Answer: (b)

Explanation: The $cis$-form of the $[Co(en)_{2}Cl_{2}]^{+}$ complex gives a pair of non-identical mirror images (enantiomorphs).

45. The magnetic properties and geometries of $[Ni(CN)_{4}]^{2-}$ and $[NiCl_{4}]^{2-}$ respectively are:

  • (a) diamagnetic, paramagnetic and tetrahedral, square planar
  • (b) paramagnetic, diamagnetic and tetrahedral, square planar
  • (c) paramagnetic, diamagnetic and square planar, tetrahedral
  • (d) diamagnetic, paramagnetic and square planar, tetrahedral.

Correct Answer: (d)

Explanation: With strong field $CN^{-},$ $Ni^{2+}$ pairs electrons to become diamagnetic and square planar ($dsp^{2}$); with weak field $Cl^{-},$ it remains paramagnetic and tetrahedral ($sp^{3}$).

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