1s² 2s² 2p⁶ 3s¹

Here's how to understand it:

* 1s²: The first energy level (n=1) has one subshell (s) which can hold up to 2 electrons. Sodium has 2 electrons in this subshell.

* 2s²: The second energy level (n=2) also has an s subshell, which holds 2 electrons.

* 2p⁶: The second energy level also has a p subshell, which can hold up to 6 electrons. Sodium has all 6 electrons in this subshell.

* 3s¹: The third energy level (n=3) starts with the s subshell, and sodium has only 1 electron in this subshell.

Key points:

* The electronic configuration describes the arrangement of electrons in an atom.

* The superscripts represent the number of electrons in each subshell.

* The outermost electron, in the 3s subshell, is responsible for sodium's chemical properties.