Potassium (K) is a metallic chemical element with atomic number 19. It has been assigned the symbol K because it's called Kalium in Latin. Its most abundant isotope is ³⁹K, 19 protons and 20 neutrons.

Potassium belongs to a group of elements called Alkali Metals, together with lithium, sodium, rubidium, caesium and francium. Like all the other alkali metals, potassium is very reactive.

One of potassium's functions within our bodies is to help transmit signals in the nervous system, via an enzyme called the sodium-potassium pump.