Question

Statement-I : Consider the following pairs of ions $(\text{Sc}^{3+}, \text{Ti}^{3+}), (\text{Ti}^{4+}, \text{Ni}^{2+}), (\text{Cu}^{2+}, \text{Zn}^{2+})$ and $(\text{Cr}^{3+}, \text{Mn}^{3+})$. Out of these pairs three pairs consist of ions that are both coloured :
Statement-II : Among the lanthanide ions $\text{Eu}^{2+}$, $\text{Gd}^{3+}$, $\text{Ce}^{4+}$ and $\text{Tb}^{4+}$, the ion $\text{Tb}^{4+}$ is the strongest reducing agent.
Choose the correct option.

• A. Both statements are true
• B. Both statements are false
• C. Statement-I is true and statement-II is false
• D. Statement-I is false and statement-II is true

Hint:

Ions with empty ($d^0$) or full ($d^{10}$) d-orbitals are colorless. In lanthanides, $+4$ ions are oxidizers and $+2$ ions are reducers as they strive for the $+3$ state.

Answer 1

The Correct Option is B

To analyze the given statements, let's consider the two primary aspects: the color of ions and the reducing strength of lanthanide ions.

1. Examining Statement-I:
   • Transition metal ions show colors mainly due to d-d transitions. Ions with partially filled d orbitals can absorb certain frequencies of light, causing them to appear colored.
   • Consider the provided ion pairs:
     • \((\text{Sc}^{3+}, \text{Ti}^{3+})\):
       • \(\text{Sc}^{3+}\) has no electrons in its d orbital (configuration: [Ar]3d⁰), hence it is colorless.
       • \(\text{Ti}^{3+}\) has one d electron (configuration: [Ar]3d¹), hence it can be colored.
     • \((\text{Ti}^{4+}, \text{Ni}^{2+})\):
       • \(\text{Ti}^{4+}\) has no d electrons (configuration: [Ar]), so it is colorless.
       • \(\text{Ni}^{2+}\) has eight d electrons (configuration: [Ar]3d⁸), thus it may be colored.
     • \((\text{Cu}^{2+}, \text{Zn}^{2+})\):
       • \(\text{Cu}^{2+}\) has nine d electrons (configuration: [Ar]3d⁹), so it is colored.
       • \(\text{Zn}^{2+}\) has a full d shell (configuration: [Ar]3d¹⁰), hence it is colorless.
     • \((\text{Cr}^{3+}, \text{Mn}^{3+})\):
       • Both \(\text{Cr}^{3+}\) (configuration: [Ar]3d³) and \(\text{Mn}^{3+}\) (configuration: [Ar]3d⁴) have partially filled d-orbitals and are colored.
   • By analysis, only one given pair, \((\text{Cr}^{3+}, \text{Mn}^{3+})\), consists of both colored ions. Thus, Statement-I is false.
2. Examining Statement-II:
   • To determine the reducing strength among lanthanide ions, recall that a reducing agent donates electrons easily.
   • The ion with a higher tendency to donate electrons is a stronger reducing agent:
   • In the given options of lanthanide ions:
     • \(\text{Ce}^{4+}\) to \(\text{Ce}^{3+}\) is a common reduction, suggesting that \(\text{Ce}^{4+}\) may act as a reducing agent. However, Ce typically acts as an oxidizing agent.
     • \(\text{Eu}^{2+}\) is known to be a strong reducing agent compared to \(\text{Tb}^{4+}\).
     • The configuration of lanthanides implies \(\text{Tb}^{4+}\) is not the strongest reducing agent; rather, its electron configuration supports its stability as \(\text{Tb}^{3+}\).
   • Statement-II incorrectly identifies \(\text{Tb}^{4+}\) as the strongest reducing agent; thus, Statement-II is false.

Conclusion: Both statements are false for the reasons outlined. Therefore, the correct answer is: Both statements are false.