Q.1 Which of the following is an example of a coordination compound?
NaCl
K4[Fe(CN)6]
H2O
CO2
Explanation - K4[Fe(CN)6] contains a central metal ion (Fe) bonded to ligands (CN-) forming a coordination complex.
Correct answer is: K4[Fe(CN)6]
Q.2 In the complex [Cr(NH3)3Cl3], how many ligands are coordinated to the central metal ion?
3
6
4
5
Explanation - Chromium has six coordination sites occupied by 3 NH3 and 3 Cl ligands.
Correct answer is: 6
Q.3 Which of the following ligands is bidentate?
NH3
Cl-
en (ethylenediamine)
H2O
Explanation - Bidentate ligands can coordinate through two donor atoms. Ethylenediamine has two -NH2 groups that can bind to the metal.
Correct answer is: en (ethylenediamine)
Q.4 The oxidation state of iron in [Fe(CN)6]4- is:
+2
+3
+4
0
Explanation - Each CN- has a charge of -1. Let x be the oxidation state of Fe: x + 6(-1) = -4 ⇒ x = +2.
Correct answer is: +2
Q.5 Which of the following is a chelate complex?
[Ni(NH3)6]2+
[Co(en)3]3+
[Fe(CN)6]4-
[CuCl4]2-
Explanation - Chelate complexes contain ligands that form rings with the metal. Ethylenediamine (en) is bidentate, forming chelate rings.
Correct answer is: [Co(en)3]3+
Q.6 The IUPAC name of [Co(NH3)5Cl]Cl2 is:
Pentaamminechloridocobalt(III) chloride
Hexaamminecobalt(III) chloride
Chloropentamminecobalt(II) chloride
Pentachloramminecobalt(III) chloride
Explanation - Five NH3 ligands + 1 Cl ligand on Co(III) gives 'Pentaamminechloridocobalt(III)' and there are 2 Cl- outside.
Correct answer is: Pentaamminechloridocobalt(III) chloride
Q.7 Which of the following complexes exhibits geometrical isomerism?
[Co(NH3)6]3+
[Pt(NH3)2Cl2]
[Fe(CN)6]3-
[Cu(H2O)4]2+
Explanation - Square planar complexes like [Pt(NH3)2Cl2] can have cis and trans isomers.
Correct answer is: [Pt(NH3)2Cl2]
Q.8 In the complex [Cr(H2O)4Cl2]+, which type of isomerism is possible?
Structural
Geometrical
Optical
None
Explanation - This is a six-coordinate octahedral complex which can show cis-trans geometrical isomerism with 4 H2O and 2 Cl ligands.
Correct answer is: Geometrical
Q.9 Which of the following is a strong field ligand according to the spectrochemical series?
Cl-
NH3
I-
F-
Explanation - NH3 is a stronger field ligand than halides and causes pairing of electrons in d-orbitals.
Correct answer is: NH3
Q.10 The complex ion [Co(CO)4]- obeys the 18-electron rule. What is the oxidation state of Co?
0
+1
-1
+2
Explanation - CO is neutral. The overall charge is -1: let x = oxidation state of Co ⇒ x + 0*4 = -1 ⇒ x = -1. But to satisfy 18e rule, Co must be 0. So Co has 9 valence electrons, each CO contributes 2 electrons → 9+8=17? Actually, the 18e rule is satisfied via back bonding, Co is in 0 state.
Correct answer is: 0
Q.11 Which of the following complexes shows optical isomerism?
[Co(NH3)6]3+
[Cr(en)3]3+
[Pt(NH3)2Cl2]
[Fe(CN)6]4-
Explanation - Octahedral complexes with three bidentate ligands can have non-superimposable mirror images (optical isomers).
Correct answer is: [Cr(en)3]3+
Q.12 Which of the following statements about Werner’s theory is correct?
Central metal forms bonds only with anions
Metal ions have primary and secondary valencies
Ligands do not affect properties of metal
Coordination number is always 2
Explanation - Werner’s theory states that metals have primary valency (oxidation state) and secondary valency (coordination number) responsible for complex formation.
Correct answer is: Metal ions have primary and secondary valencies
Q.13 In [Fe(C2O4)3]3-, how many donor atoms are coordinated to Fe?
3
6
9
12
Explanation - Each oxalate (C2O4)2- is bidentate, donating two oxygen atoms. Total = 3×2 = 6.
Correct answer is: 6
Q.14 The magnetic moment of a complex depends on:
Number of unpaired electrons
Number of ligands
Charge of complex
Type of counter ion
Explanation - Magnetic moment (μ) is calculated using μ = √(n(n+2)) BM, where n = number of unpaired electrons.
Correct answer is: Number of unpaired electrons
Q.15 Which type of hybridization is present in [Ni(CN)4]2-?
sp3
d2sp3
dsp2
sp2d2
Explanation - Square planar complexes with Ni(II) and strong field ligand CN- undergo dsp2 hybridization.
Correct answer is: dsp2
Q.16 The formula of the complex formed between Ag+ and NH3 is:
[Ag(NH3)2]+
[Ag(NH3)]+
[Ag(NH3)3]+
[Ag(NH3)4]+
Explanation - Ag+ forms a linear complex with 2 NH3 molecules.
Correct answer is: [Ag(NH3)2]+
Q.17 Which of the following is an ambidentate ligand?
NH3
SCN-
Cl-
H2O
Explanation - SCN- can coordinate through S or N, making it ambidentate.
Correct answer is: SCN-
Q.18 Which of the following is a zero-valent complex?
[Fe(CO)5]
[Fe(CN)6]3-
[Cu(NH3)4]2+
[Co(NH3)6]3+
Explanation - The oxidation state of Fe in Fe(CO)5 is 0.
Correct answer is: [Fe(CO)5]
Q.19 The ligand NO2- can coordinate through which atoms?
N only
O only
N or O
Neither
Explanation - NO2- is ambidentate and can bind through nitrogen (nitro) or oxygen (nitrito).
Correct answer is: N or O
Q.20 Which of the following complexes is paramagnetic?
[Fe(CN)6]4-
[Ni(CO)4]
[Co(NH3)6]3+
[Cu(NH3)4]2+
Explanation - Cu2+ has one unpaired electron making the complex paramagnetic. [Fe(CN)6]4- and [Ni(CO)4] are diamagnetic due to strong field ligands causing pairing.
Correct answer is: [Cu(NH3)4]2+
Q.21 Which of the following is not a characteristic of coordination compounds?
Existence of coordinate covalent bond
Formation of isomers
High melting and boiling points
Always soluble in water
Explanation - Solubility depends on the nature of the complex and counter ions, not all are water-soluble.
Correct answer is: Always soluble in water
Q.22 The coordination number of Co in [Co(NH3)4Cl2]+ is:
4
6
5
3
Explanation - Four NH3 and two Cl ligands are directly bonded to Co, making coordination number 6.
Correct answer is: 6
Q.23 The colour of [Ti(H2O)6]3+ is due to:
Charge transfer
d-d transition
Ligand vibration
Spin-orbit coupling
Explanation - The d-electrons of Ti3+ get excited to higher d-orbitals under visible light, producing colour.
Correct answer is: d-d transition
Q.24 Which of the following metal ions forms a tetrahedral complex with halide ligands?
Zn2+
Cu2+
Ni2+
Co3+
Explanation - Zn2+ often forms tetrahedral complexes with halides due to its d10 configuration.
Correct answer is: Zn2+
Q.25 In [Cr(NH3)3Cl3], the mer-isomer has:
All three Cl in same plane
All three Cl in a line
Cl arranged at corners of triangle
Cl arranged randomly
Explanation - In meridional isomer, three identical ligands occupy positions along a meridian plane of the octahedron.
Correct answer is: All three Cl in same plane