Coordination Compounds — NEET Chemistry MCQs with answers

Coordination Compounds is a Class 12 Chemistry chapter in the NEET (UG) syllabus. NEET720 has 864 reviewed practice questions on it, each with a quick answer and a step-by-step explanation. The 8 questions below are free and fixed, so you can bookmark this page; the full chapter, plus mistake tracking and spaced revision, is in the app.

Topics covered

Terminology and nomenclature · Isomerism in coordination compounds · Valence bond theory and magnetic behaviour · Crystal field theory · Stability, applications and organometallics · CFT: high spin vs low spin · Werner's theory vs modern bonding theories · IUPAC nomenclature error detection · Isomerism: geometrical isomers of [M(AB)₂X₂] type · Stability of chelates (chelate effect) · Colour of coordination compounds · Valence bond theory hybridisation and magnetic behaviour · EAN (Effective Atomic Number) rule · Ambidentate ligands and linkage isomerism · CFSE and lattice/hydration energy anomalies · Bridging ligands and polynuclear complexes · Stability constants and selective ligand extraction · 18-electron rule and organometallic stability · Optical isomerism in octahedral complexes · Jahn-Teller distortion · Coordination number and geometry prediction · Crystal field splitting in tetrahedral vs octahedral fields · Synergic bonding in metal carbonyls · Nomenclature of anionic complexes (-ate suffix) · Trans effect and its application · Magnetic moment calculation and structure determination · Polydentate ligand denticity and coordination number · Sidgwick's EAN rule limitations · Cis-platin and biological relevance of coordination chemistry · Double salts vs coordination compounds · Spectrochemical series and anomalous ligand position · Coordination compounds in extraction of metals (application) · Number of geometrical isomers: [M(AA)(BC)₂] type · Colour and d-d transitions: complexes with d0 and d10 configuration · Isomerism: ionisation isomerism · Hydrate isomerism · Nomenclature: complex cation vs complex anion within same formula · Coordination number vs oxidation number distinction · Polymerisation isomerism · Racemic mixtures and resolution of coordination complexes

8 free Coordination Compounds practice questions with answers

Choose an answer in your head before opening it. Each explanation says why the correct option is right and, where relevant, why the tempting wrong option is wrong.

1. Question 1 · easy · Isomerism in coordination compounds

   Consider the following statements distinguishing structural isomerism from stereoisomerism in coordination compounds: (I) Structural isomers differ in the connectivity of atoms/ligands (which groups are bonded where), while stereoisomers have identical connectivity but differ in spatial arrangement. (II) Ionization, linkage, hydrate, and coordination isomerism are all types of structural isomerism. (III) Geometrical and optical isomerism are types of stereoisomerism. (IV) Structural isomers and stereoisomers can never have the same molecular formula. Which statements are correct?

   • A.II and III only
   • B.I, II, III and IV
   • C.I, II and III only
   • D.I and IV only
   Show answer and explanation

   Answer: C. I, II and III only

   I, II and III correctly define and classify the two broad isomerism categories; IV is false since sharing the same molecular formula is the defining requirement for any two compounds to be isomers at all.

   I is true and is the fundamental distinction: structural isomers differ in which atoms are bonded to which (connectivity), while stereoisomers share identical connectivity but differ in 3-D spatial arrangement. II is true: ionization, linkage, hydrate/solvate, and coordination isomerism are all classified as structural (constitutional) isomerism. III is true: geometrical (cis-trans/fac-mer) and optical isomerism are the two main types of stereoisomerism in coordination chemistry. IV is false: by definition, isomers (whether structural or stereo) always share the same molecular formula — that is the very criterion that makes them isomers rather than simply different compounds.

   Common mistake: Believing isomers must differ in molecular formula rather than sharing it.

2. Question 2 · easy · Terminology and nomenclature

   In Werner's theory of coordination compounds, the primary valency of a metal ion is satisfied only by:

   • A.Neutral molecules such as NH3 or H2O, and it is non-ionizable
   • B.Other cations coordinated directly to the metal
   • C.Both anions and neutral molecules equally
   • D.Anionic groups, and it is ionizable in solution
   Show answer and explanation

   Answer: D. Anionic groups, and it is ionizable in solution

   Werner's primary valency equals the oxidation state of the metal and is satisfied exclusively by anions, which are ionizable in solution; secondary valency (coordination number) is satisfied by anions or neutral ligands and is non-ionizable.

   Werner proposed that metal ions in coordination compounds possess two types of valency. Primary (ionizable) valency corresponds to the oxidation state of the metal and is satisfied only by negatively charged ions, which dissociate in aqueous solution and can be precipitated or detected by simple tests (e.g., AgNO3 for free Cl-). Secondary (non-ionizable) valency corresponds to the coordination number, is fixed and directional, giving the complex its characteristic geometry, and can be satisfied by anions or neutral molecules. In CoCl3.6NH3 ([Co(NH3)6]Cl3), the primary valency (3) is satisfied by the three ionizable Cl- ions, while the secondary valency (6) is satisfied by the six NH3 molecules.

   Common mistake: Believing primary valency can also be satisfied by neutral ligands like NH3.

3. Question 3 · easy · Terminology and nomenclature

   Which of the following ligands is bidentate?

   • A.NH3
   • B.H2O
   • C.Cl-
   • D.H2N-CH2-CH2-NH2 (ethylenediamine)
   Show answer and explanation

   Answer: D. H2N-CH2-CH2-NH2 (ethylenediamine)

   Ethylenediamine has two nitrogen donor atoms that can simultaneously bind the same metal ion, forming a stable five-membered chelate ring, making it bidentate.

   Denticity is the number of donor atoms of a single ligand attached to the central metal ion. NH3, Cl-, and H2O each have exactly one lone pair-bearing atom available for coordination, so they are monodentate. Ethylenediamine (en), H2N-CH2-CH2-NH2, has two nitrogen atoms, each with a lone pair, positioned so both can bind the same metal simultaneously, forming a five-membered chelate ring. Hence en is bidentate.

   Common mistake: Assuming any nitrogen- or oxygen-containing ligand is automatically polydentate.

4. Question 4 · easy · Terminology and nomenclature

   An ambidentate ligand is best described as a ligand that:

   • A.Has two identical donor atoms that bind the same metal simultaneously
   • B.Simultaneously forms two separate bonds to two different metal centres, bridging them
   • C.Must always carry a negative charge to show this behaviour
   • D.Can coordinate to the metal through either of two different donor atoms, but only one at a time
   Show answer and explanation

   Answer: D. Can coordinate to the metal through either of two different donor atoms, but only one at a time

   An ambidentate ligand possesses two different donor atoms (e.g., N and O in NO2-) but uses only one of them to bind the metal in any given complex, giving rise to linkage isomerism.

   Ambidentate ligands contain two different atoms capable of donating an electron pair, but coordinate through only one of them at a time in a given complex. Classic examples are the nitrite ion (NO2-, bonds via N as nitro or via O as nitrito), thiocyanate (SCN-, via S as thiocyanato or via N as isothiocyanato), and cyanide/cyanate. This is distinct from a bidentate ligand (which uses both donor atoms simultaneously on the same metal) and from a bridging ligand (which connects two different metal centres).

   Common mistake: Confusing ambidentate with bidentate or bridging ligand behaviour.

5. Question 5 · medium · Terminology and nomenclature

   Consider the following statements about Werner's theory of coordination compounds: (I) Secondary valency is non-ionizable and is directed in space, giving the complex a definite geometry. (II) Secondary valency of a metal ion is always numerically equal to its oxidation state. (III) Ligands satisfying secondary valency may be anionic or neutral. How many of the above statements are correct?

   • A.Zero
   • B.One
   • C.Three
   • D.Two
   Show answer and explanation

   Answer: D. Two

   Statements I and III are true; II is false because secondary valency (coordination number) and oxidation state (primary valency) are independent quantities that need not be numerically equal.

   Statement I is a correct restatement of Werner's postulate that secondary valency is directional and fixed, producing the complex's geometry (e.g., octahedral for CN 6). Statement II is false: coordination number and oxidation state are determined independently — e.g., in [Co(NH3)6]Cl3, CN = 6 and oxidation state = +3 (equal by coincidence), but in [PtCl6]2-, CN = 6 while oxidation state of Pt = +4 (not equal), and in [Ag(NH3)2]+, CN = 2 while oxidation state = +1. Statement III is correct: secondary valency can be satisfied by anions (Cl-, CN-) or neutral molecules (NH3, H2O). So exactly two statements (I and III) are correct.

   Common mistake: Assuming coordination number always equals oxidation state.

6. Question 6 · medium · Terminology and nomenclature

   The coordination number of the central metal ion in a complex is most precisely defined as:

   • A.The number of ligand species surrounding the metal ion
   • B.The number of donor atoms directly bonded to the central metal ion
   • C.The oxidation number of the central metal ion
   • D.The total number of atoms present in the complex ion
   Show answer and explanation

   Answer: B. The number of donor atoms directly bonded to the central metal ion

   Coordination number counts sigma bonds from donor atoms to the metal, not the number of ligand molecules — a single hexadentate ligand like EDTA4- still gives a coordination number of 6.

   Coordination number (CN) is the number of donor atoms directly bonded to the central metal atom/ion through coordinate bonds. For monodentate ligands, CN equals the number of ligands (e.g., [Co(NH3)6]3+ has CN 6 from six NH3). However, for polydentate ligands this differs from the ligand count: [Ni(en)3]2+ has only 3 ligand molecules but CN = 6 because each en contributes 2 donor N atoms; [Ca(EDTA)]2- has just 1 ligand but CN = 6 since EDTA4- is hexadentate. This distinguishes CN from both ligand count and oxidation state.

   Common mistake: Equating coordination number with the number of ligand molecules, which fails for polydentate ligands.

7. Question 7 · medium · Terminology and nomenclature

   The correct IUPAC name of [Co(NH3)6]Cl3 is:

   • A.Hexaamminecobalt(VI) chloride
   • B.Cobalt hexaammine(III) chloride
   • C.Hexaamminecobalt(III) chloride
   • D.Hexaamminecobaltate(III) chloride
   Show answer and explanation

   Answer: C. Hexaamminecobalt(III) chloride

   Three Cl- ions balance a +3 complex cation, so cobalt is in the +3 state; ligands (ammine) are named before the metal, and no '-ate' suffix is used since the complex ion is cationic.

   Naming order: ligands (alphabetically, with multiplying prefix) then metal name then oxidation state in Roman numerals in parentheses, then the anion name. Here there are 6 NH3 ligands -> 'hexaammine'. Since three Cl- balance the charge of the complex cation, the complex ion charge is +3; as NH3 is neutral, Co must be +3. The complex ion is a cation, so the metal retains its normal name 'cobalt' (no '-ate' suffix). Full name: Hexaamminecobalt(III) chloride.

   Common mistake: Using coordination number in place of oxidation state, or adding '-ate' suffix to a cationic complex.

8. Question 8 · medium · Terminology and nomenclature

   The IUPAC name 'potassium hexacyanoferrate(II)' corresponds to the formula:

   • A.K3[Fe(CN)6]
   • B.K4[Fe(CN)6]
   • C.K2[Fe(CN)6]
   • D.K4[Fe(CN)4]
   Show answer and explanation

   Answer: B. K4[Fe(CN)6]

   With Fe in the +2 state and six CN- ligands (total charge -6), the complex ion [Fe(CN)6]4- carries a -4 charge, requiring four K+ ions to balance it: K4[Fe(CN)6].

   The name specifies: hexacyano = 6 CN- ligands, ferrate(II) = Fe with oxidation state +2 in an anionic complex. Complex ion charge = Fe oxidation state + sum of ligand charges = (+2) + 6(-1) = -4, so the complex ion is [Fe(CN)6]4-. To balance this -4 charge, four K+ counter-ions are needed, giving K4[Fe(CN)6] (potassium ferrocyanide).

   Common mistake: Confusing ferrocyanide (Fe(II), K4) with ferricyanide (Fe(III), K3).

Questions about Coordination Compounds for NEET

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