Question 1

Number of paramagnetic complexes among the following is ________. [ MnBr _4]^ 2- , [ NiCl _4]^ 2- , [ Ni(CN) _4]^ 2- , [ Ni(CO) _4], [ CoF _6]^ 3- , [ Fe(CN) _6]^ 4- , [ Mn(CN) _6]^ 3- , [ Ti(CN) _6]^

Accepted Answer

To determine the magnetic nature of the given complexes, we analyze the oxidation state, electronic configuration, and the nature of the ligands for each central metal atom/ion: 1. [ MnBr _4]^ 2- : Mn^ 2+ has a 3d^5 configuration. Br^- is a weak field ligand. The complex is tetrahedral with 5 unpaired electrons. (Paramagnetic) 2. [ NiCl _4]^ 2- : Ni^ 2+ has a 3d^8 configuration. Cl^- is a weak field ligand. The complex is tetrahedral with 2 unpaired electrons. (Paramagnetic) 3. [ Ni(CN) _4]^ 2-

Question 2

Which of the following sequences of hybridisation, geometry and magnetic nature are correct for the given coordination compounds ? A. [ NiCl _4]^ 2- - sp^3, tetrahedral, paramagnetic B. [ Ni(NH _3)_6]

Accepted Answer

In [ NiCl _4]^ 2- , Ni is in +2 oxidation state with a 3d^8 configuration. Since Cl ^- is a weak field ligand, no pairing of electrons takes place. The hybridisation is sp^3, the geometry is tetrahedral, and the presence of two unpaired electrons makes it paramagnetic. Thus, statement A is correct. In [ Ni(NH _3)_6]^ 2+ , Ni is in +2 oxidation state with a 3d^8 configuration. In an octahedral field, a d^8 ion cannot form inner orbital complexes. It undergoes sp^3d^2 hybridisation, forming an oct

Question 3

An excess of AgNO_3 is added to 100 mL of a 0.05 M solution of tetraaquadichloridochromium (III) chloride. The number of moles of AgCl precipitated will be __________ 10^ -3 . (Nearest integer)

Accepted Answer

The formula of tetraaquadichloridochromium (III) chloride is [Cr(H_2O)_4Cl_2]Cl. In this complex, there is one ionizable chloride ion present outside the coordination sphere. The dissociation reaction is: [Cr(H_2O)_4Cl_2]Cl [Cr(H_2O)_4Cl_2]^+ + Cl^- Number of moles of the complex = M V = 0.05 100 1000 = 0.005 moles. Since one mole of the complex yields one mole of chloride ions, the number of moles of Cl^- ions produced is 0.005 moles. When excess AgNO_3 is added, the chloride ions precipitate a

Question 4

Match the LIST-I with LIST-II List-I Electronic configuration of tetrahedral metal ion List-II Crystal Field Stabilization Energy ( _t) A. d^2 I. -0.6 B. d^4 II. -0.8 C. d^6 III. -1.2 D. d^8 IV. -0.4

Accepted Answer

In a tetrahedral crystal field, the d-orbitals split into a lower energy e set and a higher energy t_2 set. The energy of an electron in the e orbital is -0.6 _t and in the t_2 orbital is +0.4 _t. Since _t is generally small, tetrahedral complexes form high-spin configurations. The Crystal Field Stabilization Energy (CFSE) is given by: CFSE = (-0.6 n_e + 0.4 n_ t_2 ) _t For d^2: The configuration is e^2 t_2^0. CFSE = 2 (-0.6) + 0 = -1.2 _t (A III) For d^4: The configuration is e^2 t_2^2. CFSE =

Question 5

Which of the following are true about the energy of the given d-orbitals of a tetrahedral complex? A. d_ xy = d_ xz > d_ x^2-y^2 B. d_ xy = d_ yz > d_ z^2 C. d_ x^2-y^2 > d_ z^2 > d_ xz D. d_ x^2-y^2

Accepted Answer

In a tetrahedral complex, the five d-orbitals split into two sets due to the crystal field created by the ligands. The ligands approach the central metal ion between the axes. The d_ xy , d_ yz , and d_ xz orbitals (forming the t_2 set) point between the axes, experiencing greater repulsion from the ligands, and thus have higher energy. The d_ x^2-y^2 and d_ z^2 orbitals (forming the e set) point along the axes, experiencing lesser repulsion, and thus have lower energy. Therefore, the energy ord

Question 6

Identify the correct statements from the following A. [Fe(C_2O_4)_3]^ 3- is the most stable complex among [Fe(OH)_6]^ 3- , [Fe(C_2O_4)_3]^ 3- and [Fe(SCN)_6]^ 3- B. The stability of [Cu(NH_3)_4]^ 2+ i

Accepted Answer

Statement A is correct. The oxalate ion (C_2O_4^ 2- ) is a bidentate ligand and forms chelate rings with the central metal ion. Due to the chelate effect, [Fe(C_2O_4)_3]^ 3- is more stable than complexes formed by monodentate ligands like [Fe(OH)_6]^ 3- and [Fe(SCN)_6]^ 3- . Statement B is incorrect. Ethylenediamine (en) is a bidentate ligand and forms chelate rings, whereas NH_3 is a monodentate ligand. Therefore, [Cu(en)_2]^ 2+ is more stable than [Cu(NH_3)_4]^ 2+ due to the chelate effect. St

Question 7

The total number of unpaired electrons present in the d^3, d^4 (low spin), d^5 (high spin), d^6 (high spin) and d^7 (low spin) octahedral complex systems is _______.

Accepted Answer

In an octahedral complex, the d-orbitals split into t_ 2g and e_g levels. For d^3: Configuration is t_ 2g ^3 e_g^0. Number of unpaired electrons = 3. For d^4 (low spin): Configuration is t_ 2g ^4 e_g^0. Number of unpaired electrons = 2. For d^5 (high spin): Configuration is t_ 2g ^3 e_g^2. Number of unpaired electrons = 5. For d^6 (high spin): Configuration is t_ 2g ^4 e_g^2. Number of unpaired electrons = 4. For d^7 (low spin): Configuration is t_ 2g ^6 e_g^1. Number of unpaired electrons = 1.

Question 8

The correct statements about metal carbonyls are A. The metal-carbon bonds in metal carbonyls possess both and -character. B. Due to synergic bonding interactions between metal and CO ligand, the meta

Accepted Answer

Statement A is correct. The metal-carbon bond in metal carbonyls possesses both and character due to synergic bonding. Statement B is incorrect. The synergic bonding interaction between the metal and the CO ligand strengthens the metal-carbon bond. Statement C is correct. The metal-carbon bond is formed by the donation of a lone pair of electrons from the carbonyl carbon into a vacant orbital of the metal. Statement D is correct. The metal-carbon bond is formed by the back-donation of electrons

Question 9

Given below are two statements: Statement I: Each electron in e_g orbitals destabilizes the orbitals by +0.6 _o and each electron in the t_ 2g orbitals stabilizes the orbitals by -0.4 _o in an octahed

Accepted Answer

In an octahedral crystal field, the five degenerate d-orbitals split into two sets: a lower energy t_ 2g set and a higher energy e_g set. The energy of the t_ 2g orbitals is lowered by 0.4 _o (stabilization of -0.4 _o) and the energy of the e_g orbitals is raised by 0.6 _o (destabilization of +0.6 _o) relative to the barycenter. Hence, Statement I is correct. In the free atomic or ionic state, all five d-orbitals of a transition metal are degenerate (have the same energy). When ligands approach

Question 10

Consider the metal complexes [Ni(en)_3]^ 2+ (A), [NiCl_4]^ 2- (B) and [Ni(NH_3)_6]^ 2+ (C). Choose the CORRECT option by considering the number of unpaired electrons present in (A), (B) and (C) respec

Accepted Answer

The oxidation state of Ni in all three complexes is +2. The electronic configuration of Ni^ 2+ is [Ar] 3d^ 8 . In [Ni(en)_3]^ 2+ (A), the coordination number is 6 (octahedral geometry). The d^ 8 configuration in an octahedral field is t_ 2g ^ 6 e_ g ^ 2 , which has 2 unpaired electrons. In [NiCl_4]^ 2- (B), the coordination number is 4 with weak field Cl^ - ligands (tetrahedral geometry). The d^ 8 configuration in a tetrahedral field is e^ 4 t_ 2 ^ 4 , which has 2 unpaired electrons. In [Ni(NH_3

Question 11

Match the LIST-I with LIST-II List-I Complex ion List-II Calculated spin only magnetic moment (BM) A. [Cr(H_2O)_6]^ 2+ I. 3.87 B. [Co(H_2O)_6]^ 2+ II. 5.92 C. [Cu(H_2O)_6]^ 2+ III. 4.90 D. [Mn(H_2O)_6

Accepted Answer

The spin-only magnetic moment is given by the formula = n(n+2) BM, where n is the number of unpaired electrons. A. [Cr(H_2O)_6]^ 2+ : Chromium is in the +2 oxidation state. The electronic configuration of Cr^ 2+ is [Ar] 3d^4. Since H_2O is a weak field ligand, no pairing occurs. The number of unpaired electrons is n = 4. = 4(4+2) = 24 4.90 BM. (A III) B. [Co(H_2O)_6]^ 2+ : Cobalt is in the +2 oxidation state. The electronic configuration of Co^ 2+ is [Ar] 3d^7. With H_2O as a weak field ligand,

Question 12

Which of the following complexes will show coordination isomerism? A. [Ag(NH_3)_2][Ag(CN)_2] B. [Co(NH_3)_6][Cr(CN)_6] C. [Co(NH_3)_6][Co(CN)_6] D. [Fe(NH_3)_6][Co(CN)_6] E. [Co(NH_3)_6][Fe(CN)_6] Cho

Accepted Answer

Coordination isomerism arises from the interchange of ligands between cationic and anionic entities of different metal ions present in a complex. A. [Ag(NH_3)_2][Ag(CN)_2]: Both the complex cation and anion contain the same metal ion (Ag^+). Interchanging one ligand produces a neutral molecule [Ag(NH_3)(CN)], and interchanging both ligands yields the identical compound. Thus, it does not show coordination isomerism. B. [Co(NH_3)_6][Cr(CN)_6]: The complex contains different metal ions (Co^ 3+ and

Question 13

Match List - I with List - II. List - I Chromium (III) Complexes (en = ethylene diamine) List - II _0 (cm^ -1 ) A. [Cr(CN)_6]^ 3- I. 15,060 B. [CrF_6]^ 3- II. 17,400 C. [Cr(H_2O)_6]^ 3+ III. 22,300 D.

Accepted Answer

The crystal field splitting energy _0 depends on the strength of the ligand. According to the spectrochemical series, the order of ligand strength is F^- Thus, the order of _0 for the given complexes is [CrF_6]^ 3- Matching with the given values: [CrF_6]^ 3- has the minimum _0 = 15,060 cm^ -1 (B I). [Cr(H_2O)_6]^ 3+ has _0 = 17,400 cm^ -1 (C II). [Cr(en)_3]^ 3+ has _0 = 22,300 cm^ -1 (D III). [Cr(CN)_6]^ 3- has the maximum _0 = 26,600 cm^ -1 (A IV). This corresponds to A-IV, B-I, C-II, D-III. An

Question 14

5.33 g of CrCl_3 6H_2O, which is a 1 : 3 electrolyte, is dissolved in water and is passed through a cation exchanger. The chloride ions in the eluted solution, on treatment with AgNO_3 results in 8.61

Accepted Answer

Molar mass of CrCl_3 6H_2O = 52 + 3 35.5 + 6 18 = 266.5 g mol ^ -1 Moles of complex reacted = 5.33 266.5 = 0.02 mol Since the complex is a 1:3 electrolyte, it dissociates to give one complex cation and three chloride anions. Its formula is [Cr(H_2O)_6]Cl_3. When passed through a cation exchanger, the complex cation is exchanged, and the chloride ions pass into the eluted solution. Molar mass of AgCl = 108 + 35.5 = 143.5 g mol ^ -1 Moles of AgCl formed = 8.61 143.5 = 0.06 mol The ratio of moles o

Question 15

The correct increasing order of spin-only magnetic moment values of the complex ions [ MnBr _ 4 ]^ 2- ( A ), [ Cu ( H _ 2 O )_ 6 ]^ 2+ ( B ), [ Ni ( CN )_ 4 ]^ 2- ( C ) and [ Ni ( H _ 2 O )_ 6 ]^ 2+ (

Accepted Answer

Calculate spin-only magnetic moment using _s = n(n+2) where n is the number of unpaired electrons. For [ MnBr _4]^ 2- (A): Mn(II) in tetrahedral environment is high spin with 5 unpaired electrons. _s = 5(7) = 35 5.92 BM. For [ Cu ( H _2 O )_6]^ 2+ (B): Cu(II) has 1 unpaired electron. _s = 1(3) = 3 1.73 BM. For [ Ni ( CN )_4]^ 2- (C): Ni(II) in square planar geometry is low spin with 0 unpaired electrons. _s = 0 BM. For [ Ni ( H _2 O )_6]^ 2+ (D): Ni(II) in octahedral environment is high spin wit

Question 16

The number of isoelectronic species among Sc ^ 3+ , Cr ^ 2+ , Mn ^ 3+ , Co ^ 3+ and Fe ^ 3+ is ' n ^ . If ' n ^ moles of AgCl is formed during the reaction of complex with formula CoCl _ 3 ( en )_ 2 N

Accepted Answer

For the complex CoCl₃(en)₂NH₃, cobalt is in +3 oxidation state with electron configuration [Ar]3d⁶. In an octahedral field with strong field ligands (ethylenediamine, ammonia, chloride), Co³⁺ forms a low-spin complex with t_ 2g ^6 e_g^0 configuration. The t_ 2g orbitals consist of d_ xy , d_ xz , and d_ yz . With all 6 electrons filling the three t_ 2g orbitals, the total number of electrons in the t_ 2g orbital set is 6.

Question 17

The correct statement among the following is:

Accepted Answer

In Ni(CO)_4, Nickel is in 0 oxidation state with configuration [Ar]3d^8 4s^2. CO is a strong field ligand, causing pairing of 4s electrons into 3d orbitals, resulting in 3d^ 10 configuration. It is sp^3 hybridized and diamagnetic (zero unpaired electrons). In [Ni(CN)_4]^ 2- , Nickel is in +2 oxidation state with configuration [Ar]3d^8. CN^- is a strong field ligand, causing pairing of the two unpaired electrons in 3d orbitals. It is dsp^2 hybridized (square planar) and diamagnetic. In [NiCl_4]^

Question 18

X is the number of geometrical isomers exhibited by [ Pt ( NH _ 3 ) ( H _ 2 O ) BrCl ]. Y is the number of optically inactive isomer(s) exhibited by [ CrCl _ 2 ( ox )_ 2 ]^ 3- Z is the number of geome

Accepted Answer

For [Pt(NH_3)(H_2O)BrCl] with square planar geometry and four different ligands, geometrical isomerism arises from different positional arrangements: X = 3. For [CrCl_2(ox)_2]^ 3- , the trans isomer is optically inactive (meso compound) while cis is optically active, giving Y = 1. For [Co(NH_3)_3(NO_2)_3] in octahedral geometry, facial (fac) and meridional (mer) isomers are possible: Z = 2. Therefore, X + Y + Z = 3 + 1 + 2 = 6

Question 19

The wavelength of light absorbed for the following complexes are in the order \( (I) [ Co ( NH _3 )_6 ]^ 3+ ; (II) [ Co ( H _2 O )_6 ]^ 3+ ; (III) [ Co ( CN )_6 ]^ 3- ; (IV) [ Co ( NH _3 )_5 ( H _2 O

Accepted Answer

Wavelength of light absorbed increases as C.F.S.E of complex decreases. [Co(CN)_6]^ 3- has maximum CFSE [CoF_6]^ 3- has least CFSE Ligand field strength ; C.F.S.E Correct wavelength order. V > II > IV > I > III

Question 20

A chromium complex with a formula CrCl _ 3 6 H _ 2 O has a spin only magnetic moment value of 3.87 BM and its solution conductivity corresponds to 1: 2 electrolyte. 2.75 g of the complex solution was

Accepted Answer

The complex CrCl _3 6 H _2 O with magnetic moment 3.87 BM indicates 3.87 = n(n+2) giving n = 3 unpaired electrons, confirming Cr³⁺. A 1:2 electrolyte means structure is [ Cr(H _2 O )_5 Cl ]^ 2+ Cl _2^-. Molar mass = 52 + 5(18) + 35.5 + 6(18) = 285.5 g/mol. Moles of complex = 2.75/285.5 = 0.00963 mol. After cation exchange, 2 Cl⁻ remain per formula unit (from the 1:2 electrolyte), giving 0.00963 × 2 = 0.01926 mol of free Cl⁻. Reacting with excess AgNO₃: mass of AgCl = 0.01926 × 143.5 = 2.76 g ≈ 3

Coordination Compounds — Previous Year Questions & Solutions