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Coordination Compounds Set-9 MCQ Online Practice Test | Class 12 | Quiz Tweek

Coordination Compounds Set-9

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

Coordination Compounds is one of the most scoring chapters in Class 12 Chemistry and also forms a strong base for JEE/NEET concepts. It links ligand chemistry (coordination number, chelation, stereochemistry) with chemical stability (formation constants), bonding ideas (VBT/CFT), and real-world predictions (magnetic moments, Jahn–Teller effect, HSAB and ambidentate ligands). Mastering these MCQs improves both accuracy and conceptual speed in board and competitive exams.

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Q1. For the complex ion $[Ti(H_2O)_6]^{3+}$ , what are the oxidation state of titanium and the number of $d$ -electrons on Ti?

(A)

Oxidation state $+2$ , $d^2$

(B)

Oxidation state $+3$ , $d^1$

(C)

Oxidation state $+4$ , $d^0$

(D)

Oxidation state $+3$ , $d^2$

Q2. Consider the coordination complex $[Co(en)_2Cl_2]^+$ (en = ethylenediamine, a bidentate ligand). How many stereoisomers (geometrical plus optical) exist for this complex, and which of them are optically active?

(A)

There are two stereoisomers: cis and trans; both are optically inactive

(B)

There are four stereoisomers: two cis enantiomeric pairs and two distinct trans forms

(C)

There are three stereoisomers: one trans and two cis, but none of them are optically active

(D)

There are three stereoisomers: one trans form (achiral) and a cis enantiomeric pair (two optically active isomers)

Q3. A metal ion $M^{2+}$ reacts with ligand $L$ to form $ML_2$ according to $M^{2+} + 2L \rightleftharpoons ML_2$ with overall formation constant $\beta_2 = 1.0\times10^8$ . If the free ligand concentration $[L]$ is maintained at $1.0\times10^{-2}\ \mathrm{M}$ (ligand in large excess), what fraction of the metal is present as $ML_2$ at equilibrium?

(A)

About $99.99\%$

(B)

About $90\%$

(C)

About $9.9\%$

(D)

About $50\%$

Q4. Which of the following octahedral electronic configurations (assume high-spin where applicable) will exhibit a pronounced first-order Jahn–Teller distortion (strong elongation or compression along one axis)?

(A)

$d^1$ and $d^2$ only

(B)

$d^3$ and $d^5$ only

(C)

$d^9$ and high-spin $d^4$

(D)

$d^6$ (both high-spin and low-spin) only

Q5. Consider the complexation equilibrium $Ag^+ + 2\,NH_3 \rightleftharpoons [Ag(NH_3)_2]^+$ with overall formation constant $\beta_2 = 1.7\times10^7$ . If the total silver initially is $1.00\times10^{-3}\ \mathrm{M}$ , what minimum free ammonia concentration $[NH_3]$ is required to reduce the free $[Ag^+]$ to $1.00\times10^{-6}\ \mathrm{M}$ ? (Assume nearly all Ag is either free $Ag^+$ or in $[Ag(NH_3)_2]^+$ .)

(A)

$7.7\times10^{-2}\ \mathrm{M}$

(B)

$7.7\times10^{-3}\ \mathrm{M}$

(C)

$1.7\times10^{-3}\ \mathrm{M}$

(D)

$1.0\times10^{-5}\ \mathrm{M}$

Q6. The complex $[Fe(CN)_6]^{4-}$ is known to be low-spin due to the strong-field ligand CN $^-$ . What is the spin-only magnetic moment $\mu_\text{eff}$ (in Bohr magneton $\mu_\mathrm{B}$ ) of $[Fe(CN)_6]^{4-}$ ?

(A)

$1.73\ \mu_\mathrm{B}$

(B)

$0\ \mu_\mathrm{B}$

(C)

$2.83\ \mu_\mathrm{B}$

(D)

$4.90\ \mu_\mathrm{B}$

Q7. For an octahedral $d^4$ metal ion the high-spin (HS) configuration is $t_{2g}^3e_g^1$ and the low-spin (LS) configuration is $t_{2g}^4e_g^0$ . Using CFSE expressions $E_\text{HS}=-0.6\Delta_o$ and $E_\text{LS}=-1.6\Delta_o+P$ (where $P$ is pairing energy), determine which spin state is thermodynamically more stable when $\Delta_o=150\ \mathrm{kJ\,mol^{-1}}$ and $P=300\ \mathrm{kJ\,mol^{-1}}$ .

(A)

Low-spin (LS) is more stable
( $E_\text{LS}$ lower)

(B)

Both states are equally stable

(C)

Low-spin is more stable by $150\ \mathrm{kJ\,mol^{-1}}$

(D)

High-spin (HS) is more stable; $E_\text{HS}$ is lower by $150\ \mathrm{kJ\,mol^{-1}}$

Q8. The formation of $ML_2$ is described by $M^{2+}+2L\rightleftharpoons ML_2$ with overall formation constant $\beta_2=10^4$ . If initially $[M]_0=1.0\times10^{-3}\ \mathrm{M}$ and $[L]_0=2.0\times10^{-3}\ \mathrm{M}$ , approximately what percentage of the total metal is present as $ML_2$ at equilibrium?

(A)

$3.6\%$

(B)

$96.4\%$

(C)

$50\%$

(D)

$0.36\%$

Q9. A coordination compound with formula $[M(NH_3)_6]Cl_3$ is soluble and its molar conductance corresponds to a 1:3 electrolyte (all three Cl $^-$ are outer-sphere). The measured effective magnetic moment per metal center is $\mu_\text{eff}=4.90\ \mu_\mathrm{B}$ . Which metal (and oxidation state) is most consistent with these observations?

(A)

$\mathrm{Cr^{3+}}$ (d $^3$ )

(B)

$\mathrm{Fe^{3+}}$ (d $^5$ )

(C)

$\mathrm{Mn^{3+}}$ (d $^4$ )

(D)

$\mathrm{Co^{3+}}$ (d $^6$ ; expected low-spin with $\mu_\text{eff}\approx 0$ )

Q10. The standard potential for the couple $Fe^{3+}/Fe^{2+}$ is $E^\circ=+0.77\ \mathrm{V}$ . In the presence of CN $^-$ both ions form hexacyanide complexes with formation constants $\beta_4$ for $Fe^{2+}+6CN^-\rightleftharpoons[Fe(CN)_6]^{4-}=10^{35}$ and $\beta_3$ for $Fe^{3+}+6CN^-\rightleftharpoons[Fe(CN)_6]^{3-}=10^{20}$ . Using the relation $\Delta E=(0.0591/n)\log(\beta_4/\beta_3)$ (with $n=1$ ), what is the approximate standard potential for the complex couple $[Fe(CN)_6]^{3-}/[Fe(CN)_6]^{4-}$ ?

(A)

$+0.77\ \mathrm{V}$

(B)

$+1.66\ \mathrm{V}$

(C)

$+0.89\ \mathrm{V}$

(D)

$+0.08\ \mathrm{V}$

Q11. Calculate the spin-only magnetic moment (in Bohr magneton, $\mu_B$ ) of the complex ion $[Fe(H_2O)_6]^{3+}$ assuming it is high-spin and orbital contribution is negligible.

(A)

$2.83\ \mu_B$

(B)

$5.92\ \mu_B$

(C)

$3.87\ \mu_B$

(D)

$4.90\ \mu_B$

Q12. Consider the octahedral complexes $[Mn(CN)_6]^{3-}$ and $[MnF_6]^{3-}$ . Assuming CN $^-$ is a strong-field ligand (low-spin) and F $^-$ is a weak-field ligand (high-spin), which statement correctly describes their spin-only magnetic moments?

(A)

Both complexes have the same spin-only magnetic moment $\approx 4.90\ \mu_B$ .

(B)

The cyanide complex has the larger magnetic moment ( $\approx 4.90\ \mu_B$ ) and the fluoride complex $\approx 2.83\ \mu_B$ .

(C)

The cyanide complex is diamagnetic while the fluoride complex has $\approx 4.90\ \mu_B$ .

(D)

The fluoride complex is high-spin with four unpaired electrons (spin-only $\approx 4.90\ \mu_B$ ), whereas the cyanide complex is low-spin with two unpaired electrons (spin-only $\approx 2.83\ \mu_B$ ).

Q13. How many stereoisomers are possible for the coordination ion $[Co(en)_2Cl_2]^+$ (en = ethylenediamine, bidentate)?

(A)

Three stereoisomers: one trans (achiral) and a pair of enantiomeric cis isomers (optically active)

(B)

Two stereoisomers: one cis and one trans only

(C)

Four stereoisomers: two cis and two trans

(D)

Only one stereoisomer because identical ligands reduce possibilities

Q14. Which of the following coordination compounds are expected to exhibit optical isomerism?
I. $[Co(en)_2Cl_2]^+$

II. $[Cr(NH_3)_4Cl_2]^+$

III. $[Ni(C_2O_4)_3]^{2-}$

IV. $[Co(NH_3)_3Cl_3]$

(A)

I and II only

(B)

II and IV only

(C)

I and III only

(D)

I, III and IV

Q15. Thiocyanate (SCN $^-$ ) is ambidentate and can bind through N or S. Using HSAB concepts, predict the preferred coordination mode in complexes of $Co^{3+}$ and $Hg^{2+}$ .

(A)

Both $Co^{3+}$ and $Hg^{2+}$ bind SCN $^-$ predominantly through S

(B)

$Co^{3+}$ binds through N while $Hg^{2+}$ binds through S

(C)

$Co^{3+}$ binds through S while $Hg^{2+}$ binds through N

(D)

Both $Co^{3+}$ and $Hg^{2+}$ bind SCN $^-$ predominantly through N

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