The formation of a lithium ion from an atom is an oxidation reaction because it involves the loss of an electron from the lithium atom. When an atom loses an electron, its oxidation state increases. In the case of lithium, the oxidation state of the atom is 0. When the lithium atom loses an electron, the oxidation state of the resulting ion is +1. Therefore, the formation of a lithium ion from an atom is an oxidation reaction.