The element denoted by the letter K on the periodic table is potassium. Potassium is an essential alkali metal, which is highly reactive and has the atomic number 19. Its symbol comes from "kalium," a historical name derived from the Latin word for potash. Potassium is crucial for a variety of biological processes, including nerve function, muscle contraction, and maintaining fluid balance in cells. In nature, it is commonly found in minerals and is vital for plant growth, often provided through fertilizers. Its properties make it important in both nutritional and industrial applications.