NEET Coordination Compounds MCQs with answers

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

Both statements are correct. CN⁻ is a strong field ligand producing a large crystal field splitting (Δ₀), whereas H₂O is a weaker field ligand producing a smaller Δ₀. Since the energy of light absorbed depends directly on Δ₀, the complexes absorb different wavelengths and thus transmit different colours.

Answer: (D) 5 and 5

Moles of AgCl precipitated = 5.74 / 143.5 = 0.04 mol. From 0.02 mol of complex, 0.04 mol of AgCl is obtained, so 0.04 / 0.02 = 2 moles of Cl⁻ ions are ionisable per mole of complex. Since Co(III) has a secondary valency (coordination number) of 6, the inner sphere must contain 1 chloride ion and 5 ammonia molecules: [Co(NH₃)₅Cl]Cl₂. Hence, m = 5, and all 5 NH₃ ligands are inside the coordination sphere.

Answer: (C) 1.5 × 10⁻³ M

EDTA forms a 1:1 complex with Mg²⁺. Millimoles of EDTA used = Molarity × Volume (mL) = 0.010 M × 15.0 mL = 0.15 mmol. Since ratio is 1:1, millimoles of Mg²⁺ in 100 mL sample = 0.15 mmol. Concentration of Mg²⁺ = 0.15 mmol / 100 mL = 1.5 × 10⁻³ M.

Answer: (D) d²sp³ and 2.83 BM

In [Mn(CN)₆]³⁻, manganese is in the +3 oxidation state (3d⁴). Since CN⁻ is a strong field ligand, it causes pairing of two electrons, leaving two unpaired electrons and freeing two 3d orbitals for d²sp³ hybridization. The spin-only magnetic moment is √(2(2+2)) = √8 ≈ 2.83 BM.

Answer: (D) Complementary light in the red region is absorbed, transmitting green light

The colour of a coordination complex is the complementary colour of the light absorbed during d-d transitions. [Ni(H₂O)₆]²⁺ absorbs red light corresponding to the crystal field splitting energy (Δ₀) and transmits its complementary green light.

Answer: (B) [Cu(CN)₄]³⁻ is so stable that it yields insufficient Cu²⁺, while [Cd(CN)₄]²⁻ dissociates to exceed the Ksp of CdS

Addition of excess KCN converts Cu²⁺ to [Cu(CN)₄]³⁻ and Cd²⁺ to [Cd(CN)₄]²⁻. The tetracyanocuprate(I) complex is extremely stable and does not provide enough free Cu⁺/Cu²⁺ to exceed Ksp(Cu₂S/CuS), whereas the less stable [Cd(CN)₄]²⁻ furnishes enough Cd²⁺ to precipitate as yellow CdS.

Answer: (B) 3

When [Cr(H₂O)₅Cl]Cl₂ dissolves in water, it dissociates into one complex cation, [Cr(H₂O)₅Cl]²⁺, and two chloride anions, 2 Cl⁻. Hence, a total of 1 + 2 = 3 ions are formed per formula unit.

Answer: (A) Tetraamminecarbonatocobalt(III) perchlorate

The ligands are ammine (neutral) and carbonato (CO₃²⁻, charge -2). The counterion is perchlorate (ClO₄⁻, charge -1). Thus, the oxidation state of cobalt is +3: x + 0 - 2 = +1 ⇒ x = +3. Listing ligands alphabetically gives tetraamminecarbonatocobalt(III) perchlorate.

Answer: (B) Sodium hexafluoridoaluminate(III)

The cation (sodium) is named first without multiplier prefixes. For the complex anion, the ligands are named with 'ido' ending (hexafluorido) followed by the metal name ending in '-ate' (aluminate) and its oxidation state in Roman numerals (III).

Answer: (B) [Cr(H₂O)₆]Cl₃

Solvate (hydrate) isomerism occurs when water is involved as a solvent and can exist either inside the coordination sphere as a ligand or outside as water of crystallization. [Cr(H₂O)₆]Cl₃ exists as isomers like [Cr(H₂O)₅Cl]Cl₂·H₂O and [Cr(H₂O)₄Cl₂]Cl·2H₂O.

Answer: (B) Diamminesilver(I) dicyanidoargentate(I)

In a coordination compound containing complex cation and complex anion, the cation is named first followed by the anion. For the cationic part, the central metal retains its usual name (silver), while for the anionic part, the suffix '-ate' is appended to the Latin name (argentate). The oxidation state of silver in both coordination entities is +1.

Answer: (D) (I) < (IV) < (III) < (II)

(I) [Co(NH₃)₆]³⁺ has Co³⁺ (d⁶, strong field) with n = 0 (μ = 0 BM). (IV) [NiCl₄]²⁻ is tetrahedral Ni²⁺ (d⁸) with n = 2 (μ = 2.83 BM). (III) [Cr(H₂O)₆]³⁺ has Cr³⁺ (d³) with n = 3 (μ = 3.87 BM). (II) [FeF₆]³⁻ has Fe³⁺ (d⁵, weak field) with n = 5 (μ = 5.92 BM). Thus, the order is I (0 BM) < IV (2.83 BM) < III (3.87 BM) < II (5.92 BM).

Answer: (D) (A)-(4), (B)-(2), (C)-(1), (D)-(3)

CO₃²⁻ is a didentate dianionic ligand (A-4). Diethylenetriamine (dien) is a tridentate neutral ligand (B-2). Acetylacetonate (acac⁻) is a didentate monoanionic ligand (C-1). Thiocyanate (SCN⁻) is an ambidentate monoanionic unidentate ligand (D-3).

Answer: (A) 6

Count donor atoms bound to the metal (bidentate en and oxalate each count twice). In K₄[Fe(CN)₆] the coordination number is 6.

Answer: (B) Desferrioxamine B

Desferrioxamine B (deferoxamine) is a siderophore-based chelating agent specifically used to treat iron overload by binding excess Fe³⁺ ions to form a stable water-soluble chelate that is excreted.