Which is the non-lanthanide element ?

Options

A. La
B. Lu
C. Pr
D. Pm

Explanation

To determine which is the non-lanthanide element from the given options, we can analyze the electronic configurations of each element provided in the question.

### Step-by-Step Solution:

1. **Identify the Elements and Their Symbols:**
- A: La (Lanthanum)
- B: Lu (Lutetium)
- C: Pr (Praseodymium)
- D: Pm (Promethium)

2. **Determine the Electronic Configurations:**
- **Lanthanum (La)**: The electronic configuration is [Xe] 5d¹ 6s².
- **Lutetium (Lu)**: The electronic configuration is [Xe] 4f¹⁴ 5d¹ 6s².
- **Praseodymium (Pr)**: The electronic configuration is [Xe] 4f³ 6s².
- **Promethium (Pm)**: The electronic configuration is [Xe] 4f⁵ 6s².

3. **Classify the Elements:**
- **Lanthanum (La)**: This element is in the 5d series and does not have any electrons in the 4f subshell, making it a non-lanthanide element.
- **Lutetium (Lu)**: This element has a filled 4f subshell (4f¹⁴), thus it is classified as a lanthanide.
- **Praseodymium (Pr)**: This element has electrons in the 4f subshell (4f³), making it a lanthanide.
- **Promethium (Pm)**: This element also has electrons in the 4f subshell (4f⁵), classifying it as a lanthanide.

4. **Conclusion:**
- Based on the electronic configurations and classifications, **Lanthanum (La)** is the only non-lanthanide element among the options provided.

### Final Answer:
The non-lanthanide element is **Lanthanum (La)**.

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