Here's why:

* Atomic Number: Sodium has an atomic number of 11, meaning it has 11 protons and 11 electrons.

* Electron Configuration: The electron configuration of sodium is 2, 8, 1. This means:

* The first shell (n=1) has 2 electrons.

* The second shell (n=2) has 8 electrons.

* The third shell (n=3) has 1 electron.

* Outermost Shell: The third shell is the outermost shell, and it contains only one electron.