Which among the following actinoids does not have stable electronic configuration

Options

A. Protactinium
B. Nobelium
C. Americium
D. Lawrencium

Explanation

To determine which actinoid does not have a stable electronic configuration, we will analyze the electronic configurations of the given actinoids: protactinium, nubelium, americium, and lawrencium.

### Step 1: Identify the actinoids and their atomic numbers
- **Protactinium (Pa)**: Atomic number 91
- **Nobelium (No)**: Atomic number 102
- **Americium (Am)**: Atomic number 95
- **Lawrencium (Lr)**: Atomic number 103

### Step 2: Write down the electronic configurations
1. **Protactinium (Pa)**:
- Electronic Configuration: [Rn] 5f² 6d¹ 7s²
2. **Nobelium (No)**:
- Electronic Configuration: [Rn] 5f¹⁴ 6d¹ 7s²
3. **Americium (Am)**:
- Electronic Configuration: [Rn] 5f⁷ 6d¹ 7s²
4. **Lawrencium (Lr)**:
- Electronic Configuration: [Rn] 5f¹⁴ 6d¹ 7s²

### Step 3: Analyze the stability of the electronic configurations
- A stable electronic configuration is typically characterized by having a full or half-full subshell.
- The f subshell can hold a maximum of 14 electrons. A half-filled f subshell would have 7 electrons.

### Step 4: Evaluate each actinoid's stability
- **Protactinium (Pa)**: Has 2 electrons in the f subshell (5f²) → **Not stable**.
- **Nobelium (No)**: Has 14 electrons in the f subshell (5f¹⁴) → **Stable**.
- **Americium (Am)**: Has 7 electrons in the f subshell (5f⁷) → **Stable** (half-filled).
- **Lawrencium (Lr)**: Has 14 electrons in the f subshell (5f¹⁴) → **Stable**.

### Conclusion
Among the given actinoids, **Protactinium (Pa)** does not have a stable electronic configuration because it has only 2 electrons in the f subshell, while the others have either a full or half-full configuration.

### Final Answer
**Protactinium (Pa)** does not have a stable electronic configuration.

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