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CBSE · Class 12 · Chemistry

Coordination Compounds

Standard difficulty · 20 questions · 40 marks

Name: Date: Score: ____ / 40

Show your working for Sections B and C. Answers are on the last page — try every question first!

Section A — Choose the correct answer8 × 1 = 8 marks
1.
The number of donor atoms bound to the central metal is its:
  1. atomic number
  2. denticity
  3. oxidation state
  4. coordination number
2.
The oxidation state of Fe in K2[Fe(en)(NO2)4] is:
  1. +2
  2. +3
  3. +1
  4. +4
3.
The coordination number of Cu in [Cu(H2O)4]Cl2 is:
  1. 6
  2. 2
  3. 3
  4. 4
4.
The IUPAC name of K4[CoCl6] is:
  1. potassium hexachloridocobaltate(II)
  2. potassium hexachloridocobaltate(III)
  3. potassium hexachloridocobalt(II)
  4. tetrapotassium hexachloridocobaltate(II)
5.
The number of geometrical isomers of [Co(en)2Cl2]+ (octahedral) is:
  1. 2 (cis and trans; the cis form is optically active)
  2. none
  3. 2 (cis and trans)
  4. 3
6.
The hybridisation and shape of [Ni(CN)4]2− are:
  1. d2sp3, octahedral
  2. dsp2, square planar
  3. sp3d2, octahedral
  4. sp3, tetrahedral
7.
One mole of CrCl3·6H2O (dark green) ([Cr(H2O)4Cl2]Cl·2H2O) is treated with excess AgNO3. The number of moles of AgCl precipitated is:
  1. 3
  2. 2
  3. 1
  4. 0
8.
Assertion (A): [FeF6]3− is diamagnetic.
Reason (R): A complex is diamagnetic when all its electrons are paired and paramagnetic when some are unpaired.
  1. Both A and R are true, and R is the correct explanation of A.
  2. Both A and R are true, but R is not the correct explanation of A.
  3. A is true, but R is false.
  4. A is false, but R is true.
Section B — Short answer8 × 2 = 16 marks
9.
What is the difference between a double salt and a complex compound?
10.
For [Cu(H2O)2Cl2], give the oxidation state and coordination number of the metal, and write its IUPAC name.
11.
Write the formula of hexaaquamanganese(II) chloride.
12.
A d7 metal ion sits in an octahedral weak field. Write its t2g/e_g configuration, and find the number of unpaired electrons and the crystal field stabilisation energy (ignore pairing energy).
13.
PtCl4·2NH3 is written as [Pt(NH3)2Cl4]. How many moles of AgCl does one mole give with excess AgNO3, and how many ions does it give in solution?
14.
How many geometrical isomers does [Cr(H2O)4Cl2]+ (octahedral) have? Name them if there are any.
15.
Using valence bond theory, give the hybridisation, shape and magnetic behaviour of [CoCl4]2−.
16.
Find the spin-only magnetic moment of a d2 ion in an octahedral strong field.
Section C — Word problems4 × 4 = 16 marks
17.
Explain the bonding, shape and magnetic behaviour of [Co(NH3)6]3+ using valence bond theory.
18.
For [Zn(NH3)4]2+, find the oxidation state of the metal, its d-electron count, the hybridisation and shape, the number of unpaired electrons and the spin-only magnetic moment.
19.
Co2+ (d7) forms an octahedral complex with en (strong field) and another with H2O (weak field). For each, give the t2g/e_g configuration, the number of unpaired electrons, the magnetic moment and the CFSE (ignore pairing energy). Which is high-spin?
20.
Consider the compounds PtCl4·4NH3, PtCl4·2NH3, PtCl4·6NH3. Write each as a coordination compound, and give the moles of AgCl each gives per mole with excess AgNO3 and the number of ions in solution.
AmbifulWorksheets
Practice that never repeats
CBSE · Class 12 · Chemistry

Answer key

Coordination Compounds · AW-12C-COC-2026-V1 · For parents — fold back or tear off before handing the sheet to your child.

QAnswerWorking
1(d) coordination number—
2(a) +2the oxidation state plus the ligand charges equals the charge on the complex ion
3(d) 4count the donor atoms
4(a) potassium hexachloridocobaltate(II)ligands in alphabetical order, then the metal with its oxidation state; -ate for an anionic complex
5(a) 2 (cis and trans; the cis form is optically active)—
6(b) dsp2, square planarNCERT valence-bond example
7(c) 1only chloride ions outside the square brackets are precipitated
8(d) A is false, but R is true.A is false: it has 5 unpaired electrons. R is true.
9A double salt such as Mohr's salt dissociates completely into simple ions in water. A complex compound keeps its complex ion intact in water, e.g. K4[Fe(CN)6] gives [Fe(CN)6]4− and no Fe2+.—
10+2; 4; diaquadichloridocopper(II)oxidation state = charge of complex − sum of ligand charges
11[Mn(H2O)6]Cl2metal first in the square brackets, then the ligands; counter-ions outside
12t2g5 e_g2; 3 unpaired; CFSE = −0.8Δ0Δ0 < P: one electron in each orbital before pairing; CFSE = (−0.4 × 5 + 0.6 × 2)Δ0
130 mol AgCl; no ions (it is a non-electrolyte)ions outside the brackets are free in solution
142 (cis and trans)—
15sp3; tetrahedral; paramagnetic with 3 unpaired electrons (μ ≈ 3.87 BM)NCERT example
162 unpaired; √8 ≈ 2.83 BMt2g2 e_g0
17Co3+ is 3d6. NH3 makes the six 3d electrons pair in three orbitals, leaving two 3d orbitals empty. These, with 4s and three 4p orbitals, form d2sp3 hybrids that accept six NH3 lone pairs. The complex is octahedral, inner-orbital and diamagnetic.—
18+2; d10; sp3, tetrahedral; 0 unpaired; 0 BM (diamagnetic)oxidation state from the charge; then the valence bond picture
19with en: t2g6 e_g1, 1 unpaired, √3 ≈ 1.73 BM, CFSE −1.8Δ0; with H2O: t2g5 e_g2, 3 unpaired, √15 ≈ 3.87 BM, CFSE −0.8Δ0; the H2O complex is high-spinstrong field: pair in t2g before using e_g
20PtCl4·4NH3 = [Pt(NH3)4Cl2]Cl2: 2 AgCl, 3 ions; PtCl4·2NH3 = [Pt(NH3)2Cl4]: 0 AgCl, 0 ions; PtCl4·6NH3 = [Pt(NH3)6]Cl4: 4 AgCl, 5 ionsthe coordination number of the metal stays the same; ammonia replaces chloride inside the sphere