Sodium, periodic table Na, is a solid metal. It has 11 protons, and its most common isotope is Na23, with 12 neutrons.
Sodium should be present in many salts and minerals on the surface of Mars, and has been detected by the rovers (reference needed).
Sodium represents 0,2% of the composition of the human body. It is therefore an important requirements for a Martian settlement.
- wikipedia: https://en.wikipedia.org/wiki/Sodium