The oxidation state of an atom or ion is the number of electrons
that are taken away or given to it. Positive oxidation states
are electrons taken away and negative oxidation states are
electrons given. When tin dissolves in sulfuric acid to make
tin(II) sulfate, the tin loses two electrons and becomes a Sn2+
ion, which is tin in its +2 oxidation state. The hydrogen ion
(H+) gains an electron from the tin, changing the oxidation
state from +1 to 0. All elements have an oxidation state of 0.