In which of the following actinoid elements, 6d sub-shells is vacant?

Options

A. Pa
B. Np
C. Lr
D. Pu

Explanation

To determine which actinoid element has a vacant 6d subshell, we need to analyze the electronic configurations of the given actinoid elements. Let's go through the steps systematically.

### Step 1: Identify the electronic configurations of the actinoid elements
We will look at the electronic configurations of the actinoid elements mentioned in the question.

1. **Protactinium (Pa)**:
- Configuration: [Rn] 5f² 6d¹ 7s²
- Here, the 6d subshell has 1 electron.

2. **Neptunium (Np)**:
- Configuration: [Rn] 5f⁴ 6d¹ 7s²
- Here, the 6d subshell has 1 electron.

3. **Lawrencium (Lr)**:
- Configuration: [Rn] 5f¹⁴ 6d¹ 7s²
- Here, the 6d subshell has 1 electron.

4. **Plutonium (Pu)**:
- Configuration: [Rn] 5f⁶ 7s²
- Here, the 6d subshell is vacant (0 electrons).

### Step 2: Analyze the configurations
From the configurations analyzed above, we can see that:
- Protactinium, Neptunium, and Lawrencium all have 1 electron in the 6d subshell.
- Plutonium has no electrons in the 6d subshell, indicating that it is vacant.

### Step 3: Conclusion
The actinoid element in which the 6d subshell is vacant is **Plutonium (Pu)**.

### Final Answer
**Plutonium (Pu)** is the actinoid element with a vacant 6d subshell.

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