Lithium Lithium Lithium (from ) is a chemical element with symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the lightest metal and the lightest solid element. Like all alkali metals, lithium is highly reactive and flammable, and is stored in mineral oil. When cut, it exhibits a metallic luster, but moist air corrodes it quickly to a dull silvery gray, then black tarnish. It never occurs freely in nature, but only in (usually ionic) compounds, such as pegmatitic minerals which were once the main source of lithium. Due to its solubility
Greatest and least elements greatest elements is a special completeness property of a partial order. Further introductory information is found in the article on order theory. Greatest and least elements In mathematics, especially in order theory, the greatest element of a subset "S" of a partially ordered set (poset) is an element of "S" that is greater than every other element of "S". The term least element is defined dually, that is, it is an element of "S" that is smaller than every other element of "S". Formally, given a partially ordered set ("P", ≤), an element "g" of a subset "S" of "P"