NEETAceToday's NEET Daily

Werner theory, ligands, coordination number, denticity and chelation: NEET MCQs with answers

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

Practise Coordination Compounds freeAll Coordination Compounds questions

Free with a Google sign-in; NEET Daily needs no sign-in at all.

easy

1. In the octahedral coordination complex ion [Co(H₂O)₄Cl₂]⁺, calculate the formal oxidation state of the central Co ion:

  1. 3
  2. 4
  3. 1
  4. 2
Show answer and explanation

Answer: (A) 3

Water (H₂O) is a neutral ligand (charge = 0), and chlorine (Cl) is an anionic ligand (charge = -1). For [Co(H₂O)₄Cl₂]⁺: x + 4(0) + 2(-1) = +1. Solving gives x = +3.

Quick tip: Always sum the ligand formal charges to match the overall ionic charge.

medium

2. Which among the following species can act as a bridging ligand between two transition metal centres through lone pairs on a single donor atom?

  1. Carbon monoxide (CO)
  2. Ethylenediamine (en)
  3. Hydroxido (OH⁻)
  4. Oxalate ion (C₂O₄²⁻)
Show answer and explanation

Answer: (C) Hydroxido (OH⁻)

The hydroxido ion (OH⁻) contains multiple lone pairs on its single oxygen donor atom, allowing it to coordinate simultaneously to two metal centres to form a μ-hydroxo bridge (M-OH-M). In contrast, en and oxalate bridge (if at all) using different donor atoms.

hard

3. In the complex [Co(en)(dien)Cl]²⁺ (where en = ethylenediamine and dien = diethylenetriamine), the coordination number of cobalt and the total number of nitrogen donor atoms coordinated to it are respectively:

  1. 6 and 5
  2. 5 and 4
  3. 6 and 4
  4. 5 and 5
Show answer and explanation

Answer: (A) 6 and 5

Ethylenediamine (en) is bidentate (contributing 2 N atoms) and diethylenetriamine (dien) is tridentate (contributing 3 N atoms). Along with 1 monodentate chloride ion, total coordination number = 2 + 3 + 1 = 6, and total coordinated nitrogen donor atoms = 2 + 3 = 5.

medium

4. The coordination number of the central metal in [Cu(NH₃)₄]SO₄ is:

  1. 2
  2. 4
  3. 3
  4. 6
Show answer and explanation

Answer: (B) 4

Count donor atoms bound to the metal (bidentate en and oxalate each count twice). In [Cu(NH₃)₄]SO₄ the coordination number is 4.

easy

5. Which of the following ligands is an ambidentate ligand?

  1. Thiocyanate ion (SCN⁻)
  2. Carbonate ion (CO₃²⁻)
  3. Oxalate ion (C₂O₄²⁻)
  4. Ethylenediamine (en)
Show answer and explanation

Answer: (A) Thiocyanate ion (SCN⁻)

An ambidentate ligand is a unidentate ligand that can coordinate to a central atom through two different donor atoms. Thiocyanate (SCN⁻) can coordinate either through nitrogen (-NCS) or sulfur (-SCN).

hard

6. A 0.001 mol sample of a cobalt complex Co(NH₃)₅(SO₄)Br produces 0.001 mol of a pale cream precipitate when treated with excess AgNO₃ solution, but gives no precipitate when treated with aqueous BaCl₂. What are the primary and secondary valencies satisfied by the sulphate group in this compound?

  1. Primary valency only
  2. Secondary valency only
  3. Neither primary nor secondary valency
  4. Both primary and secondary valency
Show answer and explanation

Answer: (D) Both primary and secondary valency

Precipitation of 1 mole of AgBr per mole of complex and no BaSO₄ precipitation confirms that Br⁻ is outside the sphere while SO₄²⁻ is inside: [Co(NH₃)₅(SO₄)]Br. Since SO₄²⁻ is coordinated inside the sphere to Co(III), it satisfies both the secondary valency (coordination position) and part of the primary valency (neutralising +2 of cobalt's +3 charge).

medium

7. The coordination number of the central metal in [Co(NH₃)₆]Cl₃ is:

  1. 4
  2. 3
  3. 2
  4. 6
Show answer and explanation

Answer: (D) 6

Count donor atoms bound to the metal (bidentate en and oxalate each count twice). In [Co(NH₃)₆]Cl₃ the coordination number is 6.

medium

8. Given below are two statements: Statement I: Chelating ligands form more stable coordination complexes than comparable monodentate ligands. Statement II: Chelation leads to an overall increase in the entropy of the system (ΔS > 0) due to the release of displaced monodentate solvent molecules. In light of the above statements, choose the most appropriate answer:

  1. Both Statement I and Statement II are correct and Statement II is the correct explanation for Statement I.
  2. Both Statement I and Statement II are correct but Statement II is NOT the correct explanation for Statement I.
  3. Statement I is correct but Statement II is incorrect.
  4. Statement I is incorrect but Statement II is correct.
Show answer and explanation

Answer: (A) Both Statement I and Statement II are correct and Statement II is the correct explanation for Statement I.

Chelate complexes are thermodynamically more stable than analogous complexes with monodentate ligands (the chelate effect). This enhanced stability is predominantly driven by a favourable increase in entropy (ΔS > 0), as a single multidentate ligand displaces multiple monodentate solvent molecules, thereby increasing the total number of free species in solution.

medium

9. The coordination number of the central metal in K₃[Fe(CN)₆] is:

  1. 4
  2. 6
  3. 2
  4. 3
Show answer and explanation

Answer: (B) 6

Count donor atoms bound to the metal (bidentate en and oxalate each count twice). In K₃[Fe(CN)₆] the coordination number is 6.

medium

10. The coordination number of the central metal in [Ni(CO)₄] is:

  1. 4
  2. 3
  3. 2
  4. 6
Show answer and explanation

Answer: (A) 4

Count donor atoms bound to the metal (bidentate en and oxalate each count twice). In [Ni(CO)₄] the coordination number is 4.

medium

11. A coordination compound with empirical formula CrCl₃·6H₂O exhibits a freezing point depression in water corresponding to the production of 3 moles of particles per mole of complex. The coordination number of Cr and the number of coordinated water molecules are respectively:

  1. 6 and 6
  2. 6 and 4
  3. 4 and 4
  4. 6 and 5
Show answer and explanation

Answer: (D) 6 and 5

Production of 3 moles of ions per mole of complex indicates the formulation [Cr(H₂O)₅Cl]Cl₂·H₂O, which dissociates into [Cr(H₂O)₅Cl]²⁺ and 2 Cl⁻ (total 3 ions). The central chromium ion is surrounded by 5 H₂O molecules and 1 Cl⁻ inside the coordination sphere, giving a coordination number of 6 with 5 coordinated water molecules.

medium

12. The oxidation state of the central metal in K₃[Al(C₂O₄)₃] is:

  1. 2
  2. 0
  3. 1
  4. 3
Show answer and explanation

Answer: (D) 3

Balance the charges of the counter-ions and ligands (CN⁻, Cl⁻, C₂O₄²⁻ negative; NH₃, H₂O, CO, en neutral). The metal is +3.

Keep going with Coordination Compounds. All 429 questions with instant answers, your mistakes saved for revision and your accuracy by topic.
Start practising

Other topics in Coordination Compounds