ii

II is the Roman numeral for the number two. It is written as two consecutive I characters in the ancient Roman numeral system. The form appears in various contexts to indicate position, order, or sequence, and is commonly used in modern notation for sequencing and identification.

Common uses include labeling chapters, volumes, or installments (Chapter II, Volume II, Part II), and regnal numbers for rulers who share a name (examples include rulers designated with II). In literature and film, II is often used to denote a sequel or the second part of a series.

In chemistry and related sciences, the roman numeral II is used in parentheses after an element name to indicate a +2 oxidation state, as in iron(II) oxide. This usage is standard in older or formal nomenclature, while oxidation states can also appear as superscripts after chemical symbols (for example Fe2+). The notation reflects a system of designating valence or oxidation state rather than a standalone symbol.