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Applications in analysis, metallurgy and biological systems: NEET MCQs with answers

90 questions on this topic of Coordination Compounds (NEET 2027 syllabus). Here are 12; tap one to see its answer and explanation.

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easy

1. In the metallurgical extraction of gold (MacArthur-Forrest process), roasted gold ore is treated with a dilute aqueous solution of NaCN in the presence of air to form a soluble complex [X]. Subsequent treatment of [X] with zinc dust recovers metallic gold via displacement, forming complex [Y]. What are the formulas of [X] and [Y]?

  1. [X] = [Au(CN)₂]⁻ and [Y] = [Zn(CN)₂]
  2. [X] = [Au(CN)₄]⁻ and [Y] = [Zn(CN)₄]²⁻
  3. [X] = [Au(CN)₂]⁻ and [Y] = [Zn(CN)₄]²⁻
  4. [X] = [Au(CN)₄]³⁻ and [Y] = [Zn(CN)₆]⁴⁻
Show answer and explanation

Answer: (C) [X] = [Au(CN)₂]⁻ and [Y] = [Zn(CN)₄]²⁻

During the cyanidation process, gold is oxidized by atmospheric oxygen in cyanide solution to form dicyanoaurate(I), [Au(CN)₂]⁻. Zinc displaces gold from the complex to regenerate Au, forming tetracyanozincate(II), [Zn(CN)₄]²⁻.

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2. Excess copper in the human body occurs in Wilson's disease due to impaired copper excretion. Which chelating ligand is clinically used to coordinate and eliminate excess copper from tissues?

  1. Dimercaprol (BAL) only
  2. Desferrioxamine B
  3. Sodium nitroprusside
  4. D-Penicillamine
Show answer and explanation

Answer: (D) D-Penicillamine

NCERT states that excess of copper and iron in toxic proportions are removed by chelating ligands like D-penicillamine (for Cu) and desferrioxamine B (for Fe). D-penicillamine coordinates with copper to form a water-soluble chelate that is excreted.

hard

3. A metallurgical solution contains 0.050 mol of dissolved [Ag(S₂O₃)₂]³⁻ complex formed during photographic fixing or silver hydrometallurgy. If stoichiometric displacement is performed using metallic zinc dust according to the reaction: 2[Ag(S₂O₃)₂]³⁻ + Zn(s) → 2Ag(s) + [Zn(S₂O₃)₄]⁶⁻ (Atomic masses: Zn = 65.4 g mol⁻¹, Ag = 108.0 g mol⁻¹) What is the minimum mass of pure zinc required, and the mass of silver metal recovered?

  1. 1.635 g of Zn and 5.40 g of Ag
  2. 3.270 g of Zn and 5.40 g of Ag
  3. 1.635 g of Zn and 10.80 g of Ag
  4. 0.818 g of Zn and 2.70 g of Ag
Show answer and explanation

Answer: (A) 1.635 g of Zn and 5.40 g of Ag

According to the stoichiometry, 2 moles of [Ag(S₂O₃)₂]³⁻ react with 1 mole of Zn to yield 2 moles of Ag. For 0.050 mol of the silver complex: moles of Zn needed = 0.050 / 2 = 0.025 mol. Mass of Zn = 0.025 mol × 65.4 g mol⁻¹ = 1.635 g. Moles of Ag produced = 0.050 mol; Mass of Ag = 0.050 mol × 108.0 g mol⁻¹ = 5.40 g.

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4. Consider the following statements regarding coordination compounds in metallurgy and analysis: Statement I: The cyanide leaching process of gold is a hydrometallurgical method where gold is oxidised by atmospheric oxygen. Statement II: Gold is recovered from the solution complex [Au(CN)₂]⁻ by using metallic copper as the reducing agent. Choose the correct option:

  1. Both Statement I and Statement II are correct
  2. Statement I is correct but Statement II is incorrect
  3. Statement I is incorrect but Statement II is correct
  4. Both Statement I and Statement II are incorrect
Show answer and explanation

Answer: (B) Statement I is correct but Statement II is incorrect

Statement I is correct because native gold dissolves in dilute NaCN solution in the presence of oxygen from air to form [Au(CN)₂]⁻. Statement II is incorrect because zinc dust (not copper) is used as the reducing agent to displace gold.

easy

5. During qualitative inorganic salt analysis, adding excess potassium iodide (KI) solution to a mercuric chloride (HgCl₂) solution yields a scarlet precipitate that dissolves upon further addition of KI. Which soluble complex ion is formed in the clear solution?

  1. [Hg₂I₆]²⁻
  2. [HgI₃]⁻
  3. [HgI₆]⁴⁻
  4. [HgI₄]²⁻
Show answer and explanation

Answer: (D) [HgI₄]²⁻

Mercuric ions react with iodide ions to first precipitate scarlet red HgI₂. Upon addition of excess KI, this precipitate dissolves to form the colourless, soluble tetraiodomercurate(II) complex, [HgI₄]²⁻, which is also the active component of Nessler's reagent.

hard

6. During the detection of fluoride ions in water, the bleaching of the red-violet lake formed between zirconium(IV) and alizarin red-S is used. The bleaching occurs because:

  1. Fluoride oxidises Zr(IV) to a higher unstable oxidation state
  2. Fluoride forms an extremely stable and colourless complex [ZrF₆]²⁻, displacing the alizarin dye
  3. Fluoride precipitates as insoluble CaF₂ removing calcium co-factors
  4. Zirconium reduces fluoride to toxic fluorine gas
Show answer and explanation

Answer: (B) Fluoride forms an extremely stable and colourless complex [ZrF₆]²⁻, displacing the alizarin dye

Zirconium(IV) reacts with alizarin red-S to form a red-violet coordination lake. When fluoride ions are introduced, Zr⁴⁺ preferentially coordinates with F⁻ due to its high formation constant, yielding the stable, colourless [ZrF₆]²⁻ complex and releasing free yellow alizarin, causing the red-violet lake to bleach.

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7. In qualitative salt analysis, when an aqueous extract containing Co²⁺ ions is treated with excess potassium nitrite (KNO₂) acidified with acetic acid, a yellow precipitate of Fischer's salt is obtained. What is the chemical formula and oxidation state of cobalt in this precipitate?

  1. K₄[Co(NO₂)₆] ; Co(+2)
  2. K₃[Co(NO₂)₆] ; Co(+3)
  3. K₂[Co(NO₂)₄] ; Co(+2)
  4. K₃[Co(NO₂)₅(H₂O)] ; Co(+3)
Show answer and explanation

Answer: (B) K₃[Co(NO₂)₆] ; Co(+3)

In acetic acid medium, nitrite oxidizes Co²⁺ to Co³⁺, which then coordinates with excess NO₂⁻ to form potassium hexanitritocobaltate(III), K₃[Co(NO₂)₆], known as Fischer's salt (yellow precipitate). The oxidation state of Co is +3.

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8. In the brown ring test for the detection of nitrate (NO₃⁻) radical in analytical chemistry, what are the oxidation state of iron and the nature of the coordinated NO ligand in the brown complex [Fe(H₂O)₅(NO)]²⁺?

  1. Fe is in +1 state, and NO is coordinated as a neutral NO⁰ radical.
  2. Fe is in +2 state, and NO is coordinated as a neutral NO⁰ ligand.
  3. Fe is in +1 state, and NO is coordinated as a nitrosonium ion (NO⁺).
  4. Fe is in +3 state, and NO is coordinated as a nitroxyl ion (NO⁻).
Show answer and explanation

Answer: (C) Fe is in +1 state, and NO is coordinated as a nitrosonium ion (NO⁺).

In the brown ring complex [Fe(H₂O)₅(NO)]²⁺, electron transfer from NO to Fe(II) yields Fe(I) (d⁷ system, magnetic moment ~3.87 BM, 3 unpaired electrons) and a coordinated nitrosonium ion (NO⁺). Thus, iron has an oxidation state of +1.

easy

9. Which coordination compound is used as a homogeneous catalyst for the hydroformylation of alkenes to aldehydes (oxo process)?

  1. [RhH(CO)(PPh₃)₃]
  2. [PdCl₂(PPh₃)₂]
  3. TiCl₄ + Al(C₂H₅)₃
  4. V₂O₅
Show answer and explanation

Answer: (A) [RhH(CO)(PPh₃)₃]

The rhodium complex [RhH(CO)(PPh₃)₃], closely related to Wilkinson's catalyst, is widely used as a homogeneous catalyst in the hydroformylation (oxo process) of alkenes to aldehydes. Ziegler-Natta catalyst is heterogeneous, whereas V₂O₅ is used in the Contact process.

easy

10. Match the biological coordination compound / metalloenzyme in List-I with its primary metal ion and physiological role in List-II: List-I: (A) Chlorophyll (B) Haemocyanin (C) Vitamin B₁₂ (D) Carbonic anhydrase List-II: (I) Copper; oxygen transport in molluscs and arthropods (II) Zinc; rapid interconversion of CO₂ and HCO₃⁻ (III) Cobalt; anti-pernicious anaemia factor (IV) Magnesium; light absorption in plant photosynthesis Choose the correct match:

  1. (A)-(IV), (B)-(III), (C)-(I), (D)-(II)
  2. (A)-(IV), (B)-(I), (C)-(III), (D)-(II)
  3. (A)-(II), (B)-(I), (C)-(III), (D)-(IV)
  4. (A)-(I), (B)-(IV), (C)-(II), (D)-(III)
Show answer and explanation

Answer: (B) (A)-(IV), (B)-(I), (C)-(III), (D)-(II)

Chlorophyll contains Mg for photosynthesis (A-IV); Haemocyanin is a copper-based oxygen carrier found in molluscs/arthropods (B-I); Vitamin B₁₂ contains Co and prevents pernicious anaemia (C-III); Carbonic anhydrase is a Zn enzyme that hydrates CO₂ (D-II).

easy

11. Which of the following coordination compounds is widely utilized as a homogeneous catalyst for the hydrogenation of alkenes in industrial and synthetic organic chemistry?

  1. [Co₂(CO)₈]
  2. [PtCl₂(NH₃)₂]
  3. K[PtCl₃(C₂H₄)]
  4. [(Ph₃P)₃RhCl]
Show answer and explanation

Answer: (D) [(Ph₃P)₃RhCl]

Wilkinson catalyst, chloridotris(triphenylphosphine)rhodium(I), [(Ph₃P)₃RhCl], is a coordination compound used for the homogeneous hydrogenation of alkenes as cited in NCERT applications of coordination compounds.

easy

12. The pigment chlorophyll, responsible for photosynthesis, is a coordination compound of:

  1. Copper
  2. Magnesium
  3. Iron
  4. Cobalt
Show answer and explanation

Answer: (B) Magnesium

Chlorophyll is a magnesium complex. Haemoglobin contains iron and vitamin B₁₂ (cyanocobalamin) contains cobalt.

NCERT Class 12

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