There are 14 elements in actinoid series. Which of the following elements does not belong to this series?

Options

A. U
B. Np
C. Tm
D. Fm

Explanation

To determine which element does not belong to the actinoid series, we will analyze the atomic numbers of the given options and compare them with the range of atomic numbers that define the actinoid series.

### Step-by-Step Solution:

1. **Identify the Actinoid Series Range**:
The actinoid series consists of elements with atomic numbers ranging from 90 to 103.

2. **List the Given Options and Their Atomic Numbers**:
- **Uranium (U)**: Atomic number 92
- **Neptunium (Np)**: Atomic number 93
- **Thulium (Tm)**: Atomic number 69
- **Fermium (Fm)**: Atomic number 100

3. **Check Each Element Against the Actinoid Series Range**:
- **Uranium (92)**: Falls within the range (90-103), so it belongs to the actinoid series.
- **Neptunium (93)**: Also falls within the range (90-103), so it belongs to the actinoid series.
- **Thulium (69)**: Does not fall within the range (90-103), so it does not belong to the actinoid series.
- **Fermium (100)**: Falls within the range (90-103), so it belongs to the actinoid series.

4. **Conclusion**:
The only element that does not belong to the actinoid series is **Thulium (Tm)**.

### Final Answer:
**Thulium (Tm) does not belong to the actinoid series.**

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