Which of the following is not a lanthanoid element?

Options

A. Cerium
B. Europium
C. Lutetium
D. Thorium

Explanation

To determine which of the following elements is not a lanthanoid element, we need to identify the elements in the lanthanoid series and compare them with the options provided. The lanthanoid series consists of 15 elements with atomic numbers ranging from 57 to 71. These elements are characterized by their electronic configurations, which typically follow the pattern of Xe 4f1-14 5d0-1 6s2.

### Step-by-Step Solution:

1. **Identify the Lanthanoid Series**:
- The lanthanoid series includes the following elements:
- Lanthanum (La, 57)
- Cerium (Ce, 58)
- Praseodymium (Pr, 59)
- Neodymium (Nd, 60)
- Promethium (Pm, 61)
- Samarium (Sm, 62)
- Europium (Eu, 63)
- Gadolinium (Gd, 64)
- Terbium (Tb, 65)
- Dysprosium (Dy, 66)
- Holmium (Ho, 67)
- Erbium (Er, 68)
- Thulium (Tm, 69)
- Ytterbium (Yb, 70)
- Lutetium (Lu, 71)

2. **Analyze Each Option**:
- **Option A: Cerium (Ce)** - Atomic number 58. This is a lanthanoid element.
- **Option B: Europium (Eu)** - Atomic number 63. This is a lanthanoid element.
- **Option C: Lutetium (Lu)** - Atomic number 71. This is a lanthanoid element.
- **Option D: Thorium (Th)** - Atomic number 90. This is not a lanthanoid element.

3. **Conclusion**:
- Since Thorium (Th) with atomic number 90 does not fall within the range of 57 to 71, it is not a lanthanoid element.

### Final Answer:
**D: Thorium**

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