1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁵

Here's a breakdown:

* 1s²: The first energy level (n=1) has 2 electrons in the s orbital.

* 2s² 2p⁶: The second energy level (n=2) has 2 electrons in the s orbital and 6 electrons in the p orbital.

* 3s² 3p⁶: The third energy level (n=3) has 2 electrons in the s orbital and 6 electrons in the p orbital.

* 4s² 3d¹⁰: The fourth energy level (n=4) has 2 electrons in the s orbital and 10 electrons in the d orbital.

* 4p⁵: The fourth energy level (n=4) has 5 electrons in the p orbital.

Important Note: Remember that the filling of orbitals follows Hund's rule and the Aufbau principle. The 4s orbital fills before the 3d orbital, but the 3d orbital is actually at a slightly lower energy level.