The element of 4th period of the periodic table having maximum number of unpaired electrons in its ground state is

Options

A. `""_(20) Ca`
B. `""_(30)Zn`
C. `""_(33) As`
D. `""_(24)Cr`

Explanation

To determine the element of the 4th period of the periodic table that has the maximum number of unpaired electrons in its ground state, we will analyze the electronic configurations of the given options: Calcium, Zinc, Arsenic, and Chromium.

### Step 1: Identify the Atomic Numbers and Electronic Configurations
1. **Calcium (Ca)**: Atomic number = 20
- Electronic configuration: \( \text{[Ar]} 4s^2 \)
2. **Zinc (Zn)**: Atomic number = 30
- Electronic configuration: \( \text{[Ar]} 3d^{10} 4s^2 \)
3. **Arsenic (As)**: Atomic number = 33
- Electronic configuration: \( \text{[Ar]} 3d^{10} 4s^2 4p^3 \)
4. **Chromium (Cr)**: Atomic number = 24
- Electronic configuration: \( \text{[Ar]} 3d^5 4s^1 \)

### Step 2: Count the Unpaired Electrons
- **Calcium**:
- \( 4s^2 \) has 0 unpaired electrons (fully filled).

- **Zinc**:
- \( 3d^{10} \) and \( 4s^2 \) both have 0 unpaired electrons (both subshells are fully filled).

- **Arsenic**:
- \( 3d^{10} \) has 0 unpaired electrons, \( 4s^2 \) has 0 unpaired electrons, and \( 4p^3 \) has 3 unpaired electrons (1 electron in each of the three 4p orbitals).

- **Chromium**:
- \( 3d^5 \) has 5 unpaired electrons (one in each of the five 3d orbitals) and \( 4s^1 \) has 1 unpaired electron. Thus, total unpaired electrons = 5 + 1 = 6.

### Step 3: Compare the Number of Unpaired Electrons
- Calcium: 0 unpaired electrons
- Zinc: 0 unpaired electrons
- Arsenic: 3 unpaired electrons
- Chromium: 6 unpaired electrons

### Conclusion
The element of the 4th period with the maximum number of unpaired electrons in its ground state is **Chromium (Cr)**, with a total of 6 unpaired electrons.

### Final Answer
**Chromium (Cr)**

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