Question 1

What is the coordination number of the central metal ion in the complex [Co(NH₃)₆]³⁺?

Accepted Answer

The coordination number equals the total number of ligand donor atoms bonded to the central metal ion; six NH₃ molecules each donate one electron pair, giving coordination number 6.

Question 2

Which of the following ligands is classified as a bidentate ligand?

Accepted Answer

Ethylenediamine has two nitrogen donor atoms that can simultaneously coordinate to a central metal ion, making it a bidentate ligand.

Question 3

In the complex [CuCl₄]²⁻, what is the oxidation state of copper?

Accepted Answer

Using the oxidation state rule: copper oxidation state + 4(−1 from Cl⁻) = −2 overall charge, solving gives Cu as +2.

Question 4

The complex [Ni(CO)₄] is diamagnetic. This indicates that nickel in this complex has:

Accepted Answer

Diamagnetic complexes have no unpaired electrons; CO is a strong field ligand causing electron pairing in the d-orbitals of Ni(0).

Question 5

What is the IUPAC name of the complex [Pt(NH₃)₄]²⁺?

Accepted Answer

IUPAC nomenclature: prefix 'tetra' for four NH₃ ligands + 'ammine' + metal name 'platinum' + oxidation state (II) in parentheses + 'ion'.

Question 6

What is the coordination number of the central metal ion in the complex [Cu(NH₃)₄]²⁺?

Accepted Answer

The coordination number is determined by the number of ligand donor atoms bonded to the central metal; here four NH₃ ligands each donate one electron pair, giving coordination number 4.

Question 7

In the complex [Fe(CN)₆]³⁻, the oxidation state of iron is:

Accepted Answer

CN⁻ is a neutral ligand; with charge -3 on the complex and 6 CN⁻ ligands (each -1), the oxidation state of Fe is +3 (since +3 + 6(-1) = -3).

Question 8

Which of the following ligands is bidentate?

Accepted Answer

Ethylenediamine has two nitrogen atoms, each capable of donating an electron pair independently, making it a bidentate ligand.

Question 9

The complex [Ni(CO)₄] is diamagnetic. What is the geometry around the Ni atom?

Accepted Answer

With coordination number 4 and all d-electrons paired (diamagnetic), CO is a strong field ligand causing all electrons to pair in the d-orbitals, resulting in tetrahedral geometry for Ni(0).

Question 10

What is the IUPAC name of the complex [PtCl₂(NH₃)₂]?

Accepted Answer

In IUPAC nomenclature, ligands are listed alphabetically (ammine before chloro), followed by the metal name and oxidation state in parentheses.

Question 11

The complex [Co(NO₂)₆]³⁻ exhibits isomerism. Which type of isomerism is NOT possible for this complex?

Accepted Answer

With six identical monodentate ligands in an octahedral geometry, no chiral center exists, so optical isomerism cannot occur.

Question 12

Which of the following complexes will show the highest crystal field splitting (Δ₀)?

Accepted Answer

CN⁻ is a strong field ligand at the top of the spectrochemical series, causing maximum crystal field splitting compared to weak field ligands like F⁻, H₂O, and I⁻.

Question 13

In the complex [Zn(NH₃)₄]²⁺, if the stability constant K = 2.0 × 10⁹ at 25°C, what does this indicate about the complex?

Accepted Answer

A large stability constant (K >> 1) indicates the equilibrium strongly favors the complex form, demonstrating strong metal-ligand bonding and high stability.

Question 14

A complex ion [Co(NH₃)₅Cl]²⁺ is formed. What is the coordination number and oxidation state of cobalt in this complex?

Accepted Answer

Cobalt has 6 ligands (5 NH₃ + 1 Cl⁻) giving coordination number 6; with Cl⁻ as ligand (neutral charge) and overall +2 charge, Co oxidation state is +3.

Question 15

Which of the following complexes exhibits geometric isomerism but NOT optical isomerism?

Accepted Answer

[Pt(NH₃)₂Cl₂] in square planar geometry shows cis-trans isomerism but lacks the asymmetric centre needed for optical isomerism, whereas [Co(en)₃]³⁺ exhibits both.

Question 16

In the complex [Fe(H₂O)₆]²⁺, if the crystal field splitting energy (Δ₀) is 1.04 × 10⁻¹⁹ J, what is the wavelength of light absorbed (in nm)? (h = 6.63 × 10⁻³⁴ J·s, c = 3 × 10⁸ m·s⁻¹)

Accepted Answer

Using E = hc/λ, λ = hc/Δ₀ = (6.63 × 10⁻³⁴ × 3 × 10⁸)/(1.04 × 10⁻¹⁹) = 1910 nm.

AFCAT Coordination Compounds

Coordination Compounds — Practice Questions