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, let's follow these steps:

### Step 1: Understand the Actinoid Series
The actinoid series consists of 14 elements that range from atomic number 90 to atomic number 103. These elements are typically found in the f-block of the periodic table.

### Step 2: Identify the Elements in the Options
The options given are:
1. Uranium (U) - Atomic number 92
2. Neptunium (Np) - Atomic number 93
3. Thulium (Tm) - Atomic number 69
4. Fermium (Fm) - Atomic number 100

### Step 3: Check Each Element Against the Actinoid Series
- **Uranium (U)**: Atomic number 92, which is within the range of the actinoid series (90-103).
- **Neptunium (Np)**: Atomic number 93, also within the actinoid series.
- **Thulium (Tm)**: Atomic number 69, which is outside the range of the actinoid series.
- **Fermium (Fm)**: Atomic number 100, which is within the actinoid series.

### Step 4: Conclusion
From the analysis, Thulium (Tm) does not belong to the actinoid series as its atomic number (69) is outside the range of 90 to 103.

### Final Answer
The element that does not belong to the actinoid series is **Thulium (Tm)**.

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