Coordination Compounds — Class 12 MCQs with Answers

Coordination Compounds — important questions & MCQs with answers (Class 12 Chemistry)

6 solved questions from this chapter's difficulty levels, each with its answer and explanation. Tap an option to check yourself.

0 of 6 answered

1. Q1 of 6Easy

   Ligands are:

   ACatalystsBAcidsCLewis bases that donate electron pair to central metalDSolvents
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   Answer: Lewis bases that donate electron pair to central metal

   Explanation: A ligand donates a lone pair to the central metal to form a coordinate bond, acting as a Lewis base — not a catalyst, acid, or mere solvent, though some solvents like H₂O do double as ligands.

2. Q2 of 6Easy

   Cis-trans isomerism is shown by complexes of type:

   A[MA₂B₂] square planarB[MA₄] tetrahedralC[MA₆] octahedralD[MA₃]
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   Answer: [MA₂B₂] square planar

   Explanation: Cis-trans isomerism needs two non-equivalent positions for like ligands to occupy — square planar [MA₂B₂] has adjacent and opposite arrangements, but tetrahedral or [MA₆]-type complexes have only one possible arrangement, so they show none.

3. Q3 of 6Medium

   EDTA is a:

   

   AMonodentateBHexadentate ligandCBidentateDFree ion
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   Answer: Hexadentate ligand

   Explanation: EDTA⁴⁻ binds through six donor atoms — two N and four O — wrapping the metal in ring structures as a hexadentate chelating ligand, unlike simple bidentate ligands such as ethylenediamine, which use only two N atoms.

4. Q4 of 6Medium

   Assertion (A): Low spin configurations are rarely observed in tetrahedral complexes. Reason (R): For the same metal, the same ligands and the same metal–ligand distances, the tetrahedral splitting Δt is only about (4/9)Δo.

   ABoth A and R are true and R is the correct explanation of ABBoth A and R are true but R is not the correct explanation of ACA is true but R is falseDA is false but R is true
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   Answer: Both A and R are true and R is the correct explanation of A

   Explanation: A is true: tetrahedral complexes are almost always high spin. R is true and is the reason: because Δt is much smaller than Δo, the splitting energy is not large enough to force electrons to pair up in the lower set of orbitals.

5. Q5 of 6Hard

   Haemoglobin contains a coordination compound of:

   ACopperBIron with porphyrinCMagnesiumDZinc
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   Answer: Iron with porphyrin

   Explanation: Haemoglobin's heme group is an iron(II)–porphyrin complex, and it is the Fe²⁺ centre — not Mg²⁺ (found in chlorophyll instead) or Cu — that reversibly binds O₂ for transport.

6. Q6 of 6Hard

   Assertion (A): The complex ion [MnBr₄]²⁻, whose spin-only magnetic moment is 5.9 BM, is tetrahedral rather than square planar. Reason (R): All five 3d electrons of Mn²⁺ remain unpaired in this complex, so no 3d orbital is free for dsp² hybridisation.

   ABoth A and R are true and R is the correct explanation of ABBoth A and R are true but R is not the correct explanation of ACA is true but R is falseDA is false but R is true
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   Answer: Both A and R are true and R is the correct explanation of A

   Explanation: A is true: a moment of 5.9 BM corresponds to five unpaired electrons. R is true and is the reason: a square planar complex would need one vacant 3d orbital for dsp² hybridisation, but with five unpaired electrons every 3d orbital is occupied, so Mn²⁺ uses sp³ hybrid orbitals and the ion is tetrahedral.

Coordination Compounds notes: key concepts (Class 12 Chemistry)

Coordination Compounds covers Werner's theory, ligands and coordination number, IUPAC nomenclature, structural and stereoisomerism, and bonding by Valence Bond Theory (hybridisation, inner/outer-orbital complexes) and Crystal Field Theory (d-orbital splitting Δ₀, high- and low-spin), which together explain the colour, magnetism and shape of complexes.

Werner's theory

A metal shows primary (ionisable) valency satisfied by anions and secondary (fixed, non-ionisable) valency equal to the coordination number, satisfied by ligands.

Ligands

Lewis bases that donate a lone pair to the metal; classified as monodentate, bidentate (en), polydentate (EDTA is hexadentate) or ambidentate (NO₂⁻/ONO⁻).

Coordination number

Number of donor atoms directly bonded to the central metal, e.g. 6 in [Co(NH₃)₆]³⁺ and 4 in [Ni(CO)₄]. It fixes the geometry.

Chelate effect

Polydentate ligands form ring structures (chelates) that are far more stable than comparable monodentate complexes; the extra stability is largely entropic.

Oxidation number of metal

Found from the overall charge minus the sum of ligand charges; needed for naming and for predicting d-electron count and magnetism.

Structural isomerism

Ionisation, linkage (–NO₂/–ONO), coordination and hydrate/solvate isomerism arise from different connectivity of ligands and counter-ions.

Stereoisomerism

Geometrical cis–trans isomerism (in square-planar and octahedral) and optical isomerism (non-superimposable mirror images) come from spatial arrangement of ligands.

Valence Bond Theory

Metal uses hybrid orbitals (sp³ tetrahedral, dsp² square-planar, sp³d² outer or d²sp³ inner octahedral); inner-orbital complexes use (n−1)d and are often low-spin.

Crystal Field Theory

Ligands split the five d-orbitals; in an octahedral field into lower t₂g and higher eg separated by Δ₀, in a tetrahedral field the order is reversed.

Spectrochemical series

Ligands ranked by field strength: I⁻ < Br⁻ < Cl⁻ < F⁻ < H₂O < NH₃ < en < CN⁻ < CO; strong-field ligands give large Δ₀.

High-spin vs low-spin

If Δ₀ > pairing energy P (strong field), electrons pair up giving low-spin, few unpaired electrons; if Δ₀ < P (weak field), high-spin results.

Colour of complexes

A d-electron absorbs light of energy Δ₀ and jumps t₂g → eg; the complementary colour is seen. Larger Δ₀ shifts absorption to shorter wavelength.

Importance of complexes

Haemoglobin (Fe-porphyrin) carries O₂, chlorophyll contains Mg, cisplatin treats cancer, and EDTA complexes treat metal poisoning and hard water.