Which of the following elements of lanthanide series have highest tendency to show +2 oxidation state?

Options

A. `Eu`
B. `Gd`
C. `Tb`
D. none of these

Explanation

To determine which element of the lanthanide series has the highest tendency to show a +2 oxidation state, we will analyze the electronic configurations of the relevant lanthanides and their stability in different oxidation states.

### Step-by-Step Solution:

1. **Identify the Lanthanide Elements:**
The lanthanide series consists of 15 elements from Lanthanum (La) to Lutetium (Lu). For this question, we will focus on Europium (Eu), Gadolinium (Gd), and Terbium (Tb).

2. **Write the Electronic Configurations:**
- **Europium (Eu):**
- Atomic number: 63
- Electronic configuration: [Xe] 4f^7 6s^2
- **Gadolinium (Gd):**
- Atomic number: 64
- Electronic configuration: [Xe] 4f^7 5d^1 6s^2
- **Terbium (Tb):**
- Atomic number: 65
- Electronic configuration: [Xe] 4f^9 6s^2

3. **Analyze the Stability of Oxidation States:**
- **Europium (Eu):**
- When losing 2 electrons to form Eu^2+, it achieves the configuration of [Xe] 4f^7, which is half-filled and thus stable.
- **Gadolinium (Gd):**
- To form Gd^2+, it would need to lose 2 electrons, but it would still have 5d electrons remaining, leading to a less stable configuration.
- **Terbium (Tb):**
- To form Tb^2+, it would need to lose 2 electrons, but it would still have 4f^9 remaining, which is not particularly stable as it is neither half-filled nor fully filled.

4. **Conclusion:**
- Among the three elements, **Europium (Eu)** has the highest tendency to show a +2 oxidation state because it achieves a stable half-filled 4f^7 configuration upon losing 2 electrons.

### Final Answer:
**Europium (Eu) has the highest tendency to show a +2 oxidation state.**

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