1s² 2s² 2p⁶ 3s² 3p⁵

Here's how to understand this:

* 1s²: The first energy level (n=1) has 1 subshell (s) which can hold 2 electrons.

* 2s²: The second energy level (n=2) has 1 subshell (s) which can hold 2 electrons.

* 2p⁶: The second energy level (n=2) also has 3 subshells (p) which can hold a total of 6 electrons (2 electrons per p subshell).

* 3s²: The third energy level (n=3) has 1 subshell (s) which can hold 2 electrons.

* 3p⁵: The third energy level (n=3) also has 3 subshells (p) which hold 5 electrons.

Important Note: Chlorine has 17 electrons, and the electronic configuration reflects this.