Which of the following lanthanoids show `+2` oxidation state besides the characteristic oxidation state +3 of lanthanoids?

Options

A. Ce
B. Eu
C. Yb
D. Ho

Explanation

To determine which lanthanoids show a +2 oxidation state in addition to the characteristic +3 oxidation state, we can analyze the electronic configurations of the lanthanoids provided in the question.

### Step-by-Step Solution:

1. **Identify the Lanthanoids**: The options given are Cerium (Ce), Europium (Eu), Yttrium (Y), and Holmium (Ho).

2. **Write the Electronic Configurations**:
- **Cerium (Ce)**: Atomic number 58
- Electronic Configuration: [Xe] 4f¹ 5d¹ 6s²
- **Europium (Eu)**: Atomic number 63
- Electronic Configuration: [Xe] 4f⁷ 6s²
- **Yttrium (Y)**: Atomic number 70
- Electronic Configuration: [Xe] 4f¹⁴ 6s²
- **Holmium (Ho)**: Atomic number 67
- Electronic Configuration: [Xe] 4f¹¹ 6s²

3. **Determine the Oxidation States**:
- The characteristic oxidation state of lanthanoids is +3. However, we need to check if any of these elements can exhibit a +2 oxidation state.
- **Cerium**:
- If we consider +4 oxidation state, Ce can lose 4 electrons (2 from 6s and 2 from 5d), resulting in a stable noble gas configuration. Thus, it can show +4, but not +2.
- **Europium**:
- If we lose 2 electrons from the 6s orbital, we get 4f⁷, which is a half-filled configuration. This makes +2 oxidation state stable.
- **Yttrium**:
- If we lose 2 electrons from the 6s orbital, we get 4f¹⁴, which is a fully filled configuration. This also makes +2 oxidation state stable.
- **Holmium**:
- If we lose 2 electrons, we would have 4f¹¹, which is not a stable configuration. Thus, it does not show +2 oxidation state.

4. **Conclusion**:
- The lanthanoids that show a +2 oxidation state besides the +3 oxidation state are **Europium (Eu)** and **Yttrium (Y)**.

### Final Answer:
The lanthanoids that show +2 oxidation state besides the characteristic +3 oxidation state are **Europium (Eu)** and **Yttrium (Y)**.

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