Which of the following d-block element has half - filled penultimate as well as valence subshell ?

Options

A. Cu
B. Au
C. Ag
D. Cr

Explanation

To determine which d-block element has half-filled penultimate and valence subshells, we need to analyze the electronic configurations of the given options: Copper (Cu), Gold (Au), Silver (Ag), and Chromium (Cr).

### Step-by-Step Solution:

1. **Identify the Electronic Configurations**:
- **Copper (Cu)**: The electronic configuration is \( [Ar] 3d^{10} 4s^1 \).
- **Gold (Au)**: The electronic configuration is \( [Xe] 4f^{14} 5d^{10} 6s^1 \).
- **Silver (Ag)**: The electronic configuration is \( [Kr] 4d^{10} 5s^1 \).
- **Chromium (Cr)**: The electronic configuration is \( [Ar] 3d^5 4s^1 \).

2. **Analyze the Penultimate and Valence Subshells**:
- For **Copper**:
- Penultimate subshell (3d): \( 3d^{10} \) (fully filled)
- Valence subshell (4s): \( 4s^1 \) (half-filled)
- **Conclusion**: Not a correct option since the penultimate subshell is fully filled.

- For **Gold**:
- Penultimate subshell (5d): \( 5d^{10} \) (fully filled)
- Valence subshell (6s): \( 6s^1 \) (half-filled)
- **Conclusion**: Not a correct option since the penultimate subshell is fully filled.

- For **Silver**:
- Penultimate subshell (4d): \( 4d^{10} \) (fully filled)
- Valence subshell (5s): \( 5s^1 \) (half-filled)
- **Conclusion**: Not a correct option since the penultimate subshell is fully filled.

- For **Chromium**:
- Penultimate subshell (3d): \( 3d^5 \) (half-filled)
- Valence subshell (4s): \( 4s^1 \) (half-filled)
- **Conclusion**: This is the correct option since both the penultimate and valence subshells are half-filled.

3. **Final Answer**:
- The d-block element that has half-filled penultimate and valence subshells is **Chromium (Cr)**.