The element with the atomic symbol "Na" is sodium. It is a soft, silvery-white, highly reactive metal belonging to the alkali metals group on the periodic table, with an atomic number of 11. Sodium plays a vital role in biological systems, particularly in the functioning of nerve cells and maintaining fluid balance in the body. It is commonly found in nature, primarily in the form of sodium chloride (table salt), which is essential for human health but should be consumed in moderation. Sodium's reactivity makes it too dangerous to exist in its pure form in nature.