One of the alkali metals is POTASSIUM, which is a chemical element with the symbol K and atomic number 19. It is a soft, silvery-white metal that is highly reactive and is found in nature only in ionic salts. POTASSIUM is an essential nutrient for plants and animals, and it is the third most abundant element in the human body. It plays an important role in many biological processes, including nerve transmission, muscle contraction, and the maintenance of normal blood pressure.