Retro (Past 13 Year) JEE Main (Coordination Compounds) - Class 12 MCQ

Coloured regions of visible light (VIBGYOR) are arranged in the increasing order of wavelength or decreasing order of energy

This suggests that L₄ will absorbs higher energy wavelength followed by L₂, L₃ and L₁
Since, higher absorbed energy corresponds to greater extent of crystal field splitting and thus, higher field strength of the ligand Hence, the increasing order of ligand strength of the four ligands is
L₁ < L₃ < L₂ < L₄

Optical isomerism is exhibited by only those complexes which lacks elements of symmetry.
[Co(NH₃)₃CI₃] shows facial as well as meridional isomerism. But both the forms contain plane of symmetry.
Thus, this complex does not exhibit optical isomerism.

Two Br, two (en) and one Cr are parts of complex. Charge on the complex is

Thus, complex ion is [Cr(en)₂Br₂]⁺.
Since, anion is bromide thus, complex is [Cr(en)₂Br₂]Br.

The outer orbital electronic configuration of Cr is 3d³ 4s°.
The orbital diagram is represented in the figure
Here,indicates lone-pair of NH₃ donated to Cr.
(a) d²sp³-hybridisation , octahedral. Thus, correct.
(b) There are three unpaired electrons, hence paramagnetic Thus, correct.
(c) d²sp³-inner orbital complex , thus in correct.
(d) Due to ionisable Cl^- ions, white precipitate with AgNO₃, thus correct.

[NiCI₄]^2- ; oxidation number of Ni, x - 4 = - 2
x = + 2, Ni₍₂₈₎ [Ar] 3d⁸, 4s²

sp³-hybrid orbitals, tetrahedral. Since, Cl is a weak ligand, thus unpaired electrons are not paired. Lone pairs from 4CI^- are accommodated in four sp³ hybrid orbitats.
n = unpaired electron = 2, paramagnetic
Magnetic moment (spin only)

Based on spectrochemical series, ligands arranged in increasing order of crystal field strength are as

NH₃ < en < CN^- < CO

Complex [Co(en)₃]³⁺ has no plane of symmetry and centre of symmetry. That’s why, it is optically active.

Linkage isomers are caused due to the presence of ambidentate ligands.
[Pd(PPh₃)₂(NCS)₂] and [Pd(PPh₃)₂(SCN)₂] are linkage isomers due to SCN, an ambidentate ligand.
Thus, SCN can linked to Pd by both N as well as S through their lone pairs.

en,   is bidentate ligand.
 is also bidentate ligand.
Hence, coordination number of the element E in the given complex comes out to be 6.
The complex can be ionised as
[E(en)₂(C₂O₄)] NO₂ →[E(en)₂ (C₂O₄)]⁺ NO₂^- 
Oxidation number, x + 0 + (- 2) = + 1
x = 3

CFSE (crystal field splitting energy) for octahedral complex, Δ_o depends on the strength of negative ligand, Spectrochemically, it has been found that the strength of splitting is as follows :

NCS^- > H₂O > O^2- > ox^2- > OH^- > F^- > Cl^- > SCN^- > S^2- > Br^- > l^-

Cl^- is aweak ligand but Cl^- cause the pairing of electrons with large Pt²⁺ and consequently give dsp² hybridisation and square planar geometry.

Fe(CO)₅ is an organometallic coordinated compound in which electrons from d-orbital of Fe are partially transferred to antibonding molecular orbitals (π) of CO. This type of bonding is called π-back bonding.

Thus, Fe(CO)₅ possesses both σ and π-character.

The IUPAC name for the complex
[Co(NO₂)(NH₃)₅]CI₂
Pentammine nitrito-N-cobalt (III) chloride 

28^Ni = [Ar] 4s², 3d⁸
Ni²⁺ = [Ar] 3d⁸

Nickel has two unpaired electrons and geometry is tetrahedral due to sp³ hybridisation.

(a) d⁵ in strong field
n = unpaired electron = 1

Lanthanide contraction is due to poor shielding of one of 4f electron by another in the subshell.

Due to lanthanoid contraction, the atomic radii of the elements belonging to the same group of the 2nd and 3rd transition series become same. Thus, ₄₀Zr (160 pm) and ₇₂Hf (159 pm) have almost same radii.

K₃[Fe(CN)₆]
Cation Anion Oxidation state of Fe in anion = + 3
Thus, it is potassium hexacyanoferrate (III).

Thus, least paramagnetism is (a).

Mirror image is not superimposable, hence optical isomerism is possible.

Coordination number is the maximum covalency shown by a metal or metal ion. It is the maximum number of ligands attached to metal by sigma bonds or coordinate bonds.

All the given compounds exhibit geometrical (cis and trans isomers) but only cis isomer of [Co (en)₂CI₂]⁺ possess optical isomers (d and /) due to the presence of symmetrical didentate, en [ethylenediamine],

Number of unpaired electrons in [Fe(CN)₆]^4- is zero.
Thus, magnetic moment =
(n = unpaired electrons)

In this case also, NH₃ is a strong ligand but electrons remain unpaired, since only one orbital is left vacant in 3d. Thus, [Ni(NH₃)₆]²⁺ 

In acidic solutions, N-atoms of NH₃ donates their lone pair electrons to protons forming NH₄⁺ ions.
Therefore, lone pair electrons of NH₃ are not available for forming the complex with copper ions.

The oxidation state of nickel is 

The oxidation state of nickel is
K₄[Ni(CN)₄] → 4K⁺ + [Ni(CN)₄]^4-
[Ni(CN)₄]^4- , x + (4 x - 1) = - 4 
or x - 4 = - 4 or x = 0

[Cr(NH₃)₅NO₂]Cl₂ (pentam m inenitritochromium (III) chloride) exhibits linkage isomerism as—NO₂ is am bid entate ligand. Isomer is [Cr(NH₃)₅ONO] Cl₂.