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Coordination Compounds — NEET & JEE MCQs with answers
Coordination compounds contain a central metal atom or ion bonded to a definite number of ligands (ions or molecules). Key topics include Werner's theory, IUPAC nomenclature, isomerism (geometrical, optical, linkage, coordination, ionisation, solvate), bonding theories (valence bond theory and crystal field theory), magnetic properties, colour, and the importance of coordination compounds in analytical chemistry, metallurgy, biological systems, industry and medicine.
Topics in this chapter
- 5.1 Werner's Theory of Coordination Compounds
- 5.2 Definitions of Some Important Terms Pertaining to Coordination Compounds
- 5.3 Nomenclature of Coordination Compounds
- 5.4 Isomerism in Coordination Compounds
- 5.5 Bonding in Coordination Compounds
- 5.6 Bonding in Metal Carbonyls
- 5.7 Importance and Applications of Coordination Compounds
Free practice questions
Which statement about $[\mathrm{CoF_6}]^{3-}$ and $[\mathrm{Co(C_2O_4)_3}]^{3-}$ is correct?
- A. Both are paramagnetic with four unpaired electrons
- B. The first is diamagnetic and the second paramagnetic with four unpaired electrons
- C. Both are diamagnetic
- D. The first is paramagnetic with four unpaired electrons and the second is diamagnetic
Show answer
Answer: D — Option D is correct. Cobalt is $+3$ ($d^6$) in both — three didentate oxalate ions supply $3\times(-2)=-6$, giving an overall $-3$. NCERT states that $[\mathrm{CoF_6}]^{3-}$ is paramagnetic with four unpaired electrons while $[\mathrm{Co(C_2O_4)_3}]^{3-}$ is diamagnetic.
NCERT Class 12 Chemistry Part-1 · Ch 5 · §5.5.2 ("is paramagnetic with four unpaired electrons while [Co(C2O4)3]")
$\mathrm{PdCl_2\cdot 4NH_3}$ gives 2 mol AgCl per mole with excess $\mathrm{AgNO_3}$. The secondary valence of palladium in it is
- A. 2
- B. 6
- C. 8
- D. 4
Show answer
Answer: D — Option D is correct. Two of the chlorides are precipitated, so they are ionisable counter ions; the four ammonia molecules alone occupy the secondary valences, giving a secondary valence of 4 — the value printed in the solution to Example 5.1.
NCERT Class 12 Chemistry Part-1 · Ch 5 · §5.1 ("On the basis of the following observations made with aqueous solutions, assign secondary valences to metals in the following compounds")
In the metal-to-ligand interaction in a metal carbonyl, the electron pair from the filled metal d orbital is accepted by
- A. The filled bonding $\pi$ orbital of carbon monoxide
- B. The $\sigma^*$ orbital of carbon monoxide
- C. A lone-pair orbital on the oxygen atom
- D. The vacant antibonding $\pi^*$ orbital of carbon monoxide
Show answer
Answer: D — Option D is correct: NCERT states that the M–C $\pi$ bond is formed by the donation of a pair of electrons from a filled $d$ orbital of metal into the vacant antibonding $\pi^*$ orbital of carbon monoxide. It is not the bonding $\pi$ orbital, not a $\sigma^*$ orbital, and not an oxygen lone-pair orbital.
NCERT Class 12 Chemistry Part-1 · Ch 5 · §5.6 ("of metal into the vacant antibonding p*")
In both $\mathrm{[Co(NH_3)_5(SO_4)]Br}$ and $\mathrm{[Co(NH_3)_5Br]SO_4}$, the oxidation number of cobalt is:
- A. $+2$ in both compounds
- B. $+3$ in both compounds
- C. $+3$ in the first and $+2$ in the second
- D. $+2$ in the first and $+3$ in the second
Show answer
Answer: B — Option B is correct. For $\mathrm{[Co(NH_3)_5(SO_4)]Br}$: $x + 5(0) + (-2) + (-1) = 0$ gives $x = +3$. For $\mathrm{[Co(NH_3)_5Br]SO_4}$: $x + 5(0) + (-1) + (-2) = 0$ also gives $x = +3$. Ionisation isomers have the same overall formula, so the metal's oxidation number cannot change.
NCERT Class 12 Chemistry Part-1 · Ch 5 · §5.4.5 ("isomers [Co(NH3)5(SO4)]Br and [Co(NH3)5Br]SO4.")
In $\mathrm{[Ag(NH_3)_2][Ag(CN)_2]}$ the silver of the anionic part is named
- A. silver
- B. silverate
- C. argentate
- D. argentum
Show answer
Answer: C — The name NCERT prints is diamminesilver(I)dicyanidoargentate(I): the Latin stem argent- with the -ate ending is used because that silver sits in the complex anion. Option C is correct, while silver without a suffix is the form used for the cationic part.
NCERT Class 12 Chemistry Part-1 · Ch 5 · §5.3 ("diamminesilver(I)dicyanidoargentate(I)")
According to §5.2, ligands may be
- A. simple ions, small molecules, larger molecules or even macromolecules such as proteins
- B. only simple negative ions
- C. only neutral small molecules
- D. only macromolecules such as proteins
Show answer
Answer: A — Option A is correct. The text says ligands may be simple ions such as $\mathrm{Cl^-}$, small molecules such as $\mathrm{H_2O}$ or $\mathrm{NH_3}$, larger molecules such as $\mathrm{H_2NCH_2CH_2NH_2}$ or $\mathrm{N(CH_2CH_2NH_2)_3}$, or even macromolecules such as proteins.
NCERT Class 12 Chemistry Part-1 · Ch 5 · §5.2 ("larger molecules such as H2NCH2CH2NH2 or N(CH2CH2NH2)3 or even macromolecules, such as proteins")
Which pigment, responsible for photosynthesis, does NCERT cite as a coordination compound of magnesium?
- A. Chlorophyll
- B. Haemoglobin
- C. Cyanocobalamine
- D. Carbonic anhydrase
Show answer
Answer: A — Option A is correct. NCERT names chlorophyll as "the pigment responsible for photosynthesis" and a coordination compound of magnesium. Haemoglobin is the iron-containing red pigment of blood, cyanocobalamine contains cobalt, and carbonic anhydrase is an enzyme, not a photosynthetic pigment.
NCERT Class 12 Chemistry Part-1 · Ch 5 · §5.7 ("systems. The pigment responsible for photosynthesis, chlorophyll,")
$[\mathrm{Mn(CN)_6}]^{3-}$ and $[\mathrm{MnCl_6}]^{3-}$ have magnetic moments corresponding to how many unpaired electrons respectively?
- A. Four and two
- B. Two and four
- C. One and five
- D. Five and one
Show answer
Answer: B — Option B is correct. Manganese is $+3$ in both ($d^4$). NCERT states that $[\mathrm{Mn(CN)_6}]^{3-}$ has the magnetic moment of two unpaired electrons while $[\mathrm{MnCl_6}]^{3-}$ has a paramagnetic moment of four unpaired electrons — the inner-orbital and outer-orbital results for a $d^4$ ion.
NCERT Class 12 Chemistry Part-1 · Ch 5 · §5.5.2 ("has magnetic moment of two unpaired electrons while [MnCl6]")
Which of the following homoleptic carbonyls named by NCERT contains a metal–metal bond?
- A. $\mathrm{[Ni(CO)_4]}$
- B. $\mathrm{[Fe(CO)_5]}$
- C. $\mathrm{[Cr(CO)_6]}$
- D. $\mathrm{[Mn_2(CO)_{10}]}$
Show answer
Answer: D — Option D is correct: $\mathrm{[Mn_2(CO)_{10}]}$ is made of two $\mathrm{Mn(CO)_5}$ units joined by a Mn–Mn bond. $\mathrm{[Ni(CO)_4]}$, $\mathrm{[Fe(CO)_5]}$ and $\mathrm{[Cr(CO)_6]}$ are mononuclear and so cannot contain a metal–metal bond.
NCERT Class 12 Chemistry Part-1 · Ch 5 · §5.6 ("Mn(CO)5 units joined by a Mn - Mn bond")
When the thiocyanate ligand binds to a metal through its nitrogen atom, the linkage is written as:
- A. M-SCN
- B. M-ONO
- C. M-CNS
- D. M-NCS
Show answer
Answer: D — Option D is correct. NCERT states that $\mathrm{NCS^-}$ may bind through the nitrogen to give M-NCS or through sulphur to give M-SCN.
NCERT Class 12 Chemistry Part-1 · Ch 5 · §5.4.3 ("nitrogen to give M-NCS or through sulphur to give M-SCN.")
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