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Coordination Compounds Set-1 MCQ Online Practice Test | Class 12 | Quiz Tweek

Coordination Compounds Set-1

Practice Important MCQs for Coordination Compounds — Chemistry, Class 12.

Coordination compounds form a core part of Class 12 Chemistry and frequently appear in board and competitive exams because they connect electronic structure (d-orbitals), geometry, ligand field strength, magnetism, stereochemistry, and stability constants. Mastery of concepts like oxidation state, hybridisation, CFSE/spin-only moments, and cis/trans and optical isomerism helps solve both direct reasoning and calculation-based questions quickly and accurately.

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Q1. Calculate the spin-only magnetic moment (in Bohr magneton, $\mu_{\rm so}$ ) of the complex $[NiCl_4]^{2-}$ assuming ideal tetrahedral geometry. Use $\mu_{\rm so}=\sqrt{n(n+2)}\,\mu_B$ , where $n$ is the number of unpaired electrons.

(A)

$1.73\ \mu_B$

(B)

$4.90\ \mu_B$

(C)

$2.83\ \mu_B$

(D)

$0\ \mu_B$

Q2. A metal M forms successive complexes with ligand L: $M+L\rightleftharpoons ML\ (K_1)$ , $ML+L\rightleftharpoons ML_2\ (K_2)$ , $ML_2+L\rightleftharpoons ML_3\ (K_3)$ . If $K_1=10^4,\ K_2=10^5,\ K_3=10^3$ and the free ligand concentration is $[L]=10^{-2}\ \mathrm{M}$ , what percentage of total metal is present as $ML_3$ ? (Assume $[L]$ remains effectively constant.)

(A)

$90.9\%$

(B)

$99.9\%$

(C)

$50.0\%$

(D)

$9.09\%$

Q3. For an octahedral $d^6$ metal ion the low-spin state is favored when $\Delta_o>P$ (pairing energy $P$ ). Given $P=130\ \text{kJ mol}^{-1}$ , $\Delta_o(\text{X})=200\ \text{kJ mol}^{-1}$ and $\Delta_o(\text{Y})=120\ \text{kJ mol}^{-1}$ , which statement is correct?

(A)

Both complexes with X and Y ligands will be low-spin.

(B)

Both complexes will be high-spin.

(C)

Only the complex with ligand Y will be low-spin.

(D)

Only the complex with ligand X will be low-spin.

Q4. How many stereoisomers (counting enantiomers separately) exist for the complex $[Co(en)_2Cl_2]^+$ , and which of them are optically active?

(A)

Two stereoisomers; both optically inactive.

(B)

Three stereoisomers in total; a pair of cis enantiomers are optically active while the trans isomer is achiral.

(C)

Four stereoisomers; all are optically active.

(D)

Three stereoisomers; all three are optically active.

Q5. Which of the following statements about $[Ni(CN)_4]^{2-}$ and $[NiCl_4]^{2-}$ is/are correct? (i) Both have $d^8$ electronic configuration. (ii) $[Ni(CN)_4]^{2-}$ is square planar and diamagnetic. (iii) $[NiCl_4]^{2-}$ is tetrahedral and paramagnetic with two unpaired electrons. (iv) Both complexes have identical magnetic properties.

(A)

(i), (ii) and (iii) only

(B)

(i) and (iv) only

(C)

(ii) and (iv) only

(D)

All four statements (i)–(iv)

Q6. For the hexaaquairon(II) ion $[Fe(H_2O)_6]^{2+}$ in aqueous solution, assume an octahedral high-spin configuration. Using the spin-only formula $\mu_{\text{spin}}=\sqrt{n(n+2)}\ \mathrm{BM}$ where $n$ is the number of unpaired electrons, what is the expected spin-only magnetic moment (in Bohr magnetons, BM)?

(A)

$2.83\ \mathrm{BM}$

(B)

$3.87\ \mathrm{BM}$

(C)

$4.90\ \mathrm{BM}$

(D)

$5.92\ \mathrm{BM}$

Q7. At 25°C the stepwise formation constants for successive coordination of two ammonia molecules to $Cu^{2+}$ are $K_1=1.0\times10^{3}$ and $K_2=1.0\times10^{2}$ for the equilibria

Cu^{2+}+NH_3\rightleftharpoons[Cu(NH_3)]^{2+}\quad(K_1)

[Cu(NH_3)]^{2+}+NH_3\rightleftharpoons[Cu(NH_3)_2]^{2+}\quad(K_2).

If initially $[Cu^{2+}]_0=1.0\times10^{-3}\ \mathrm{M}$ and $[NH_3]_0=1.0\ \mathrm{M}$ and higher coordination is negligible, estimate the equilibrium concentration of free $Cu^{2+}$ (use the overall $K_f=K_1K_2$ and approximations where appropriate).

(A)

$9.9\times10^{-4}\ \mathrm{M}$

(B)

$1.0\times10^{-6}\ \mathrm{M}$

(C)

$1.0\times10^{-4}\ \mathrm{M}$

(D)

$1.0\times10^{-8}\ \mathrm{M}$

Q8. For a metal ion with $d^4$ electronic configuration in an octahedral ligand field, the high-spin (HS) state has configuration $t_{2g}^3e_g^1$ and the low-spin (LS) state $t_{2g}^4e_g^0$ . Using crystal field splitting energy $\Delta_o$ and pairing energy $P$ , which condition correctly predicts that the low-spin state is energetically favoured over the high-spin state?

(A)

$\Delta_o > P$

(B)

$\Delta_o > 2P$

(C)

$\Delta_o < P$

(D)

$\Delta_o > \dfrac{1}{2}P$

Q9. Assertion (A): The complex $[Fe(CN)_6]^{3-}$ is thermodynamically more stable (larger formation constant) than $[FeF_6]^{3-}$ because cyanide is a stronger ligand than fluoride and forms stronger metal–ligand bonding.
Reason (R): Cyanide can act as a $\pi$ ‑acceptor (it accepts electron density from filled metal $t_{2g}$ orbitals into its $\pi^*$ orbitals, i.e., metal→ligand backbonding), whereas fluoride is a poor $\pi$ ‑acceptor; this additional $\pi$ ‑interaction stabilizes complexes with CN $^-$ .
Choose the correct option:

(A)

Both A and R are true but R does not explain A.

(B)

Both A and R are true and R is the correct explanation of A.

(C)

A is true but R is false.

(D)

A is false but R is true.

Q10. The coordination complex $[Co(NH_3)_4Cl_2]NO_3$ is experimentally found to be diamagnetic. Using valence bond theory, determine the most probable oxidation state of cobalt and the hybridisation of the central metal orbitals used for bonding in this complex.

(A)

Oxidation state $+3$ ; hybridisation $d^2sp^3$ (inner $d$ )

(B)

Oxidation state $+2$ ; hybridisation $sp^3d^2$ (outer $d$ )

(C)

Oxidation state $+3$ ; hybridisation $sp^3d^2$ (outer $d$ )

(D)

Oxidation state $+2$ ; hybridisation $d^2sp^3$ (inner $d$ )

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