Question

Identify the pair of ions which act as good reducing agents.

• A. \(Ce^{4+}, Yb^{2+}\)
• B. \(Ce^{4+}, Tb^{4+}\)
• C. \(Ce^{3+}, Tb^{2+}\)
• D. \(Eu^{2+}, Yb^{2+}\)

Hint:

Among lanthanoids, Eu$^{2+}$ and Yb$^{2+}$ are strong reducing agents because they readily convert into the more stable +3 state.

Answer 1

The Correct Option is D

Concept: A good reducing agent donates electrons easily and gets oxidised. In lanthanoids: \[ Eu^{2+} \rightarrow Eu^{3+} + e^- \] and \[ Yb^{2+} \rightarrow Yb^{3+} + e^- \] occur easily. So they behave as strong reducing agents.

Step 1: Check Option (A) \[ Ce^{4+} \] is actually a strong oxidising agent because it tends to gain electrons. So incorrect.

Step 2: Check Option (B) Both \[ Ce^{4+} \] and \[ Tb^{4+} \] are oxidising agents. So incorrect.

Step 3: Check Option (C) \[ Ce^{3+} \] is stable and not a strong reducing agent. So incorrect.

Step 4: Check Option (D) \[ Eu^{2+} \] and \[ Yb^{2+} \] easily lose one electron to form stable \(+3\) oxidation state. Thus both act as good reducing agents. \[ \boxed{\text{Option (D) is correct}} \] Therefore, the correct answer is: \[ \boxed{(D)} \]