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1. The coordination number of a central metal atom/ion in a complex is defined as:
A. The number of ligand donor atoms directly bonded to the central atom
B. The number of ligands regardless of donor atoms
C. The overall charge on the complex ion
D. The number of electrons in the d-orbital
Answer: A. The number of ligand donor atoms directly bonded to the central atom
Explanation: Coordination number counts the sigma bonds formed between donor atoms of ligands and the central metal atom.
2. According to Werner's theory, the primary (ionizable) valency of a metal ion is satisfied by:
A. Negative ions
B. Neutral molecules only
C. Positive ions
D. Pairs of ligands
Answer: A. Negative ions
Explanation: Werner proposed that primary valency corresponds to the metal's oxidation state and is satisfied by anions.
3. EDTA (ethylenediaminetetraacetate) is a well-known example of a:
A. Hexadentate ligand
B. Monodentate ligand
C. Bidentate ligand
D. Ambidentate ligand
Answer: A. Hexadentate ligand
Explanation: EDTA can bind to a metal ion through six donor atoms (four oxygen and two nitrogen atoms), making it hexadentate.
4. Which theory best explains the colour and magnetic properties of coordination compounds?
A. Crystal field theory
B. VSEPR theory
C. Simple molecular orbital theory of diatomics
D. The octet rule
Answer: A. Crystal field theory
Explanation: Crystal field theory explains d-orbital splitting in a ligand field, accounting for colour (d-d transitions) and magnetic behaviour.
5. In IUPAC nomenclature of coordination compounds, the names of ligands are listed:
A. In alphabetical order
B. In order of their charge
C. In order of size
D. In order of the central atom's atomic number
Answer: A. In alphabetical order
Explanation: IUPAC rules require ligand names to be cited alphabetically, regardless of their charge or the number of each type present.
6. A ligand capable of linking to the central metal atom through two different donor atoms (though only one at a time) is called an/a:
A. Ambidentate ligand
B. Chelating ligand
C. Bidentate ligand
D. Polydentate ligand
Answer: A. Ambidentate ligand
Explanation: Ambidentate ligands like NO2⁻ and SCN⁻ have more than one potential donor atom but bind through only one at a time.
7. Which of the following is classified as a strong field ligand?
A. CN⁻
B. I⁻
C. F⁻
D. H2O
Answer: A. CN⁻
Explanation: CN⁻ causes large crystal field splitting and lies at the strong-field end of the spectrochemical series, typically giving low-spin complexes.
8. The geometry of the complex [Ni(CO)4] is:
A. Tetrahedral
B. Square planar
C. Octahedral
D. Linear
Answer: A. Tetrahedral
Explanation: In [Ni(CO)4], nickel is in the zero oxidation state with an sp3 hybridization, giving a tetrahedral geometry.
9. Sidgwick's EAN rule stands for the:
A. Effective Atomic Number rule
B. Electron Affinity Number rule
C. Electron Arrangement Number rule
D. Effective Atomic Neutron rule
Answer: A. Effective Atomic Number rule
Explanation: The Effective Atomic Number rule predicts the stability of a complex based on whether the metal attains the electronic configuration of the next noble gas.
10. Linkage isomerism in coordination compounds is commonly shown by ambidentate ligands such as:
A. NO2⁻
B. Cl⁻
C. NH3
D. H2O
Answer: A. NO2⁻
Explanation: NO2⁻ can coordinate through either the nitrogen atom (nitro) or an oxygen atom (nitrito), giving rise to linkage isomers.
11. Which coordination compound is widely used as an anticancer drug in chemotherapy?
A. Cisplatin, cis-[PtCl2(NH3)2]
B. K4[Fe(CN)6]
C. [Ni(CO)4]
D. [Co(NH3)6]Cl3
Answer: A. Cisplatin, cis-[PtCl2(NH3)2]
Explanation: Cisplatin, a square planar platinum(II) complex, is a well-established chemotherapy drug used to treat various cancers.
12. The oxidation state of iron in the complex ion [Fe(CN)6]⁴⁻ is:
A. +2
B. +3
C. 0
D. +6
Answer: A. +2
Explanation: Since each CN⁻ carries a charge of -1 and the overall complex ion charge is -4, iron must be in the +2 oxidation state (Fe + 6(-1) = -4).
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