Correct electronic configuration of Cu and Cr are ____.

The correct answer is Option (2) → $3d^{10} 4s^1$ and $3d^5 4s^1$ respectively

The correct electronic configurations of Cr and Cu are exceptions to the general filling order due to stability of half-filled and fully-filled d-orbitals.

 

• Copper (Cu)
• Atomic number = 29
• Expected configuration: [Ar] 3d⁹ 4s²
• But copper gains stability when the 3d subshell becomes completely filled.
• Thus, one electron shifts from 4s to 3d:
• Actual configuration: [Ar] 3d¹⁰ 4s¹
• Completely filled subshells also have extra stability.

 

• Chromium
•  Atomic number = 24
• Expected configuration: [Ar] 3d⁴ 4s²
• However, chromium attains extra stability when the 3d subshell becomes half-filled.
• Thus, one electron from 4s shifts to 3d:
• Actual configuration: [Ar] 3d⁵ 4s¹
• Half-filled subshells have greater stability due to symmetrical distribution and exchange energy.