CBSE Class 12 Chemistry: Coordination Compounds — Important Questions with Answers 2026

Short Answer Questions (2-3 Marks)

• Q: What are coordination compounds? Define: (i) coordination number, (ii) ligand, (iii) central metal ion.
  Ans: Coordination compounds contain a central metal atom/ion bonded to surrounding molecules/ions (ligands) by coordinate bonds. (i) Coordination number: Total number of ligand donor atoms directly bonded to the central metal. Example: [Co(NH₃)₆]³⁺ has CN = 6. (ii) Ligand: A molecule/ion that donates electron pair(s) to the metal. Monodentate: NH₃, Cl⁻, H₂O. Bidentate: en (ethylenediamine), C₂O₄²⁻. (iii) Central metal ion: The metal atom/ion to which ligands are attached. Example: Co³⁺ in [Co(NH₃)₆]³⁺.
• Q: Write the IUPAC name: (i) [Co(NH₃)₅Cl]Cl₂, (ii) K₃[Fe(CN)₆], (iii) [Pt(NH₃)₂Cl₂].
  Ans: (i) Pentaamminechloridocobalt(III) chloride. (ii) Potassium hexacyanidoferrate(III). (iii) Diamminedichloridoplatinum(II). IUPAC rules: Ligands listed alphabetically, anionic ligands end in 'o' (chlorido, cyanido), neutral ligands keep name (ammine for NH₃, aqua for H₂O), metal oxidation state in Roman numerals in parentheses.
• Q: Explain Crystal Field Theory for octahedral complexes.
  Ans: CFT: Ligands are treated as point charges/dipoles that interact with d-orbitals of central metal. In octahedral field: d-orbitals split into two sets — t₂g (dxy, dxz, dyz — lower energy) and eg (dx²-y², dz² — higher energy). Energy difference = Δ₀ (crystal field splitting energy). Strong field ligands (CN⁻, CO) → large Δ₀ → low spin complex (electrons pair in t₂g first). Weak field ligands (Cl⁻, F⁻) → small Δ₀ → high spin complex (electrons fill all orbitals singly first). Spectrochemical series: I⁻ < Br⁻ < Cl⁻ < F⁻ < OH⁻ < H₂O < NH₃ < en < NO₂⁻ < CN⁻ < CO.

Exam Tips for This Chapter

• Revise all definitions and laws from Coordination Compounds — commonly asked as 1-2 mark questions
• Practice diagrams related to Coordination Compounds — neat labelled diagrams carry 2-3 marks
• For numericals, always show formula → substitution → answer with correct units
• Previous year analysis shows Coordination Compounds carries significant marks in the board exam