Electronic configuration of Cr is

Options

A. `3d^5 4s^1`
B. `3d^6 4s^0`
C. `3d^4 4s^2`
D. `3d^5 4s^0`

Answer

To determine the electronic configuration of chromium (Cr), which has an atomic number of 24, we follow these steps:

### Step-by-Step Solution:

1. **Identify the Atomic Number**:
- The atomic number of chromium is 24. This means that a neutral chromium atom has 24 electrons.

2. **Fill the Electron Shells**:
- We fill the electron shells according to the Aufbau principle, which states that electrons occupy the lowest energy orbitals first.

3. **Order of Filling Orbitals**:
- The order of filling is as follows:
- 1s, 2s, 2p, 3s, 3p, 4s, 3d

4. **Fill the Orbitals**:
- Start filling the orbitals:
- 1s: 2 electrons → 1s²
- 2s: 2 electrons → 2s²
- 2p: 6 electrons → 2p⁶
- 3s: 2 electrons → 3s²
- 3p: 6 electrons → 3p⁶
- 4s: 2 electrons → 4s²
- 3d: Fill the 3d orbital next.

5. **Adjust for Stability**:
- Normally, after filling 4s², we would fill 3d with 2 electrons (3d²). However, chromium has a unique electron configuration due to stability reasons.
- Instead of 4s² 3d², chromium prefers to have a half-filled 3d subshell for extra stability.
- Therefore, we take one electron from 4s and place it in 3d.

6. **Final Configuration**:
- The final electronic configuration of chromium is:
- 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d⁵

### Conclusion:
The electronic configuration of chromium (Cr) is **1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d⁵**.