The most common lanthanoid is :

Options

A. lanthanum
B. cerium
C. samarium
D. plutonium

Answer

To solve the question regarding the most common lanthanoid from the given options (lanthanum, cerium, samarium, and plutonium), we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: We need to identify which of the given elements is the most common lanthanoid.

2. **Identify the Elements**: The options provided are:
- Lanthanum (La)
- Cerium (Ce)
- Samarium (Sm)
- Plutonium (Pu)

3. **Know the Lanthanoids**: The lanthanoids (or lanthanides) are a series of 15 chemical elements from lanthanum (atomic number 57) to lutetium (atomic number 71) in the periodic table.

4. **Determine Commonality**: Among the lanthanoids, cerium (Ce) is known to be the most abundant and commonly found in nature compared to lanthanum, samarium, and plutonium.

5. **Check Atomic Numbers**:
- Lanthanum (La) - Atomic number 57
- Cerium (Ce) - Atomic number 58
- Samarium (Sm) - Atomic number 62
- Plutonium (Pu) - Atomic number 94 (not a lanthanoid)

6. **Conclusion**: Based on the information above, cerium is the most common lanthanoid.

### Final Answer:
The most common lanthanoid is **Cerium (Ce)**.

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