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Coordination Compounds

16 NEET-UG practice questions on Coordination Compounds, part of Chemistry. The first 16 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

  1. Question 1 · Hard

    Count all the stereoisomers, including enantiomers, of the octahedral ion [Co(en)(NH₃)₂Cl₂]⁺.

    1. A3
    2. B2
    3. C4
    4. D6
    Show answer

    Answer: C · 4

    The en ligand spans two cis positions. There are three geometrical arrangements: NH₃ groups trans (Cl cis), Cl groups trans (NH₃ cis), and the all-cis form. Only the all-cis form lacks a plane of symmetry, so it exists as two enantiomers, giving 1 + 1 + 2 = 4. Check: of six ways to place two NH₃ on the four free sites, the four all-cis placements reduce to one enantiomeric pair.

    • A: This counts the geometrical isomers but forgets the enantiomer of the all-cis form.
    • B: This counts only the two forms with one pair of ligands trans.
    • D: This counts every placement of NH₃ on the free sites without removing identical ones.

    Remember this

    Count geometrical isomers first, then double only those without a plane of symmetry.

  2. Question 2 · Medium

    Arrange these ligands in increasing order of the crystal field splitting they produce with a given metal ion. A. C₂O₄²⁻ B. CO C. Br⁻ D. en

    1. AC, D, A, B
    2. BC, A, D, B
    3. CA, C, D, B
    4. DC, A, B, D
    Show answer

    Answer: B · C, A, D, B

    The spectrochemical series runs I⁻ < Br⁻ < SCN⁻ < Cl⁻ < S²⁻ < F⁻ < OH⁻ < C₂O₄²⁻ < H₂O < NCS⁻ < edta⁴⁻ < NH₃ < en < CN⁻ < CO. So Br⁻ < C₂O₄²⁻ < en < CO.

    • A: This places en below oxalate, though nitrogen donors like en split more than oxygen donors.
    • C: This places oxalate below bromide, though halides like Br⁻ are the weakest ligands.
    • D: This places CO below en, though CO is the strongest ligand in the series.

    Remember this

    Halides sit at the weak end, oxygen donors in the middle, en and NH₃ above them, and CN⁻ and CO at the strong end.

  3. Question 3 · Medium

    Ignoring pairing energy, what is the crystal field stabilisation energy of the high-spin complex [Fe(H₂O)₆]²⁺? (Atomic number of Fe = 26)

    1. A−2.4 Δ₀
    2. B−0.4 Δ₀
    3. C−1.6 Δ₀
    4. D−0.6 Δ₀
    Show answer

    Answer: B · −0.4 Δ₀

    Fe²⁺ is d⁶, and high spin gives t₂g⁴ e_g². CFSE = 4(−0.4 Δ₀) + 2(+0.6 Δ₀) = −1.6 Δ₀ + 1.2 Δ₀ = −0.4 Δ₀.

    • A: This is the low-spin value, t₂g⁶, which does not apply to this high-spin complex.
    • C: This adds up the t₂g electrons but leaves out the e_g electrons.
    • D: This is the value for high-spin d⁴, which results from miscounting the d electrons of Fe²⁺.

    Remember this

    Each t₂g electron contributes −0.4 Δ₀ and each e_g electron +0.6 Δ₀.

  4. Question 4 · Medium

    Given below are two statements: Statement I: [Ni(CN)₄]²⁻ is square planar and diamagnetic, with dsp² hybridisation. Statement II: [NiCl₄]²⁻ is also square planar and diamagnetic. Choose the correct answer.

    1. AStatement I is incorrect but Statement II is correct
    2. BBoth Statement I and Statement II are correct
    3. CBoth Statement I and Statement II are incorrect
    4. DStatement I is correct but Statement II is incorrect
    Show answer

    Answer: D · Statement I is correct but Statement II is incorrect

    CN⁻ is a strong field ligand, so the two unpaired 3d electrons of Ni²⁺ pair up, freeing a 3d orbital for dsp² bonding. Cl⁻ is weak and causes no pairing, so [NiCl₄]²⁻ is tetrahedral (sp³) with two unpaired electrons.

    • A: Statement I is right and Statement II is wrong, not the reverse.
    • B: Statement II is wrong, because [NiCl₄]²⁻ is tetrahedral and paramagnetic.
    • C: Statement I is right, so both cannot be incorrect.

    Remember this

    Four-coordinate Ni²⁺ is square planar and diamagnetic with CN⁻, but tetrahedral and paramagnetic with Cl⁻.

  5. Question 5 · Easy

    Choose the correct IUPAC name of [Pt(NH₃)₄Cl₂]Cl₂.

    1. ATetraamminedichloridoplatinum(IV) chloride
    2. BTetraamminedichloridoplatinate(IV) chloride
    3. CDichloridotetraammineplatinum(IV) chloride
    4. DTetraamminedichloridoplatinum(II) chloride
    Show answer

    Answer: A · Tetraamminedichloridoplatinum(IV) chloride

    Ligands are named in alphabetical order, so ammine comes before chlorido. The two outer chloride ions give the complex ion a +2 charge: x + 0 + 2(−1) = +2, so x = +4. A cationic complex keeps the plain metal name, platinum.

    • B: This uses the -ate ending, which belongs only to an anionic complex.
    • C: This puts chlorido before ammine, which breaks the alphabetical rule.
    • D: This takes the oxidation state as +2 by ignoring the two coordinated chlorides.

    Remember this

    Ligands go alphabetically, the oxidation state comes from the charge balance, and only an anionic complex takes the -ate ending.

  6. Question 6 · Easy

    Facial and meridional isomers are possible for which of these octahedral species?

    1. A[Cr(NH₃)₅Cl]²⁺
    2. B[Cr(NH₃)₄Cl₂]⁺
    3. C[Cr(NH₃)₃Cl₃]
    4. D[Cr(en)₃]³⁺

    Answer and explanation in LearnFree account

  7. Question 7 · Medium

    Consider these statements about isomerism. A. cis-[Co(en)₂Cl₂]⁺ is optically active. B. trans-[Co(en)₂Cl₂]⁺ is optically active. C. [Co(en)₃]³⁺ exists as a pair of enantiomers. D. fac-[Co(NH₃)₃Cl₃] is optically active. Which statements are correct?

    1. AB and D only
    2. BA and C only
    3. CA, C and D only
    4. DA, B and C only

    Answer and explanation in LearnFree account

  8. Question 8 · Hard

    Arrange these complex ions in increasing order of spin-only magnetic moment. (Atomic number of Fe = 26) A. [Fe(H₂O)₆]²⁺ B. [Fe(CN)₆]⁴⁻ C. [FeF₆]³⁻ D. [Fe(CN)₆]³⁻

    1. AB, D, A, C
    2. BD, B, A, C
    3. CB, D, C, A
    4. DB, A, D, C

    Answer and explanation in LearnFree account

  9. Question 9 · Medium

    A solution containing 0.01 mol of [Cr(H₂O)₅Cl]Cl₂·H₂O is treated with excess AgNO₃ solution. What mass of AgCl precipitates? (Ag = 108, Cl = 35.5)

    1. A2.87 g
    2. B4.305 g
    3. C1.435 g
    4. D2.16 g

    Answer and explanation in LearnFree account

  10. Question 10 · Medium

    Match List-I with List-II. List-I (Complex) A. [Co(NH₃)₆]³⁺ B. [CoF₆]³⁻ C. [Ni(CO)₄] D. [Ni(CN)₄]²⁻ List-II (Hybridisation of the metal) I. sp³ II. dsp² III. d²sp³ IV. sp³d²

    1. AA-IV, B-III, C-I, D-II
    2. BA-IV, B-III, C-II, D-I
    3. CA-III, B-IV, C-II, D-I
    4. DA-III, B-IV, C-I, D-II

    Answer and explanation in LearnFree account

  11. Question 11 · Easy

    What is the spin-only magnetic moment of the complex ion [Cr(NH₃)₆]³⁺? (Atomic number of Cr = 24)

    1. A4.90 BM
    2. B2.83 BM
    3. C3.87 BM
    4. D1.73 BM

    Answer and explanation in LearnFree account

  12. Question 12 · Medium

    Assertion A: An aqueous solution of [Ti(H₂O)₆]³⁺ is violet. Reason R: Its single d electron is excited from t₂g to e_g by absorbing visible light. Choose the correct answer.

    1. ABoth A and R are correct but R is not the correct explanation of A
    2. BA is not correct but R is correct
    3. CA is correct but R is not correct
    4. DBoth A and R are correct and R is the correct explanation of A

    Answer and explanation in LearnFree account

  13. Question 13 · Hard

    Four cobalt(III) complex ions are drawn. Which of them are optically active?

    Figure: MedExams
    Four octahedral cobalt ions labelled A to D with chloride, ammine and bidentate ethane-1,2-diamine ligands in different arrangements.
    1. AB, C and D only
    2. BC only
    3. CA, B and C only
    4. DB and C only

    Answer and explanation in LearnFree account

  14. Question 14 · Easy

    Drawings I and II show two forms of the octahedral complex [Co(NH₃)₃Cl₃]. Identify each form.

    Figure: MedExams
    Two octahedral drawings labelled I and II around cobalt, each with three chloride and three ammine ligands in different arrangements.
    1. AI is facial, II is meridional
    2. BBoth are meridional
    3. CI is meridional, II is facial
    4. DBoth are facial

    Answer and explanation in LearnFree account

  15. Question 15 · Medium

    The bars give approximate Δo values of four octahedral Cr(III) complexes [CrL₆]. Match List-I with List-II. List-I (bar) A. Bar A B. Bar B C. Bar C D. Bar D List-II (ligand L) I. H₂O II. CN⁻ III. Cl⁻ IV. NH₃

    Figure: MedExams
    Bar chart of crystal field splitting for four chromium complexes A, B, C and D, with values 22, 14, 26 and 18 thousand reciprocal centimetres.
    1. AA-I, B-III, C-II, D-IV
    2. BA-II, B-III, C-IV, D-I
    3. CA-IV, B-III, C-II, D-I
    4. DA-IV, B-I, C-II, D-III

    Answer and explanation in LearnFree account

  16. Question 16 · Medium

    Which option correctly gives a complex with the d-electron filling drawn in the figure and its spin-only magnetic moment?

    Figure: MedExams
    Crystal field splitting diagram with three lower t2g orbitals and two upper eg orbitals, with spin arrows showing the electrons.
    1. A[CoF₆]³⁻, 5.92 BM
    2. B[Co(NH₃)₆]³⁺, 4.90 BM
    3. C[CoF₆]³⁻, 2.83 BM
    4. D[CoF₆]³⁻, 4.90 BM

    Answer and explanation in LearnFree account

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