Most
p-block elements have both
positive and negative oxidation states.
- The maximum is the last digit of the group number (except for oxygen and fluorine for which the maximum is 0).
- The minimum is the Group Number - 18.
The
elemental form (oxidation state 0) of these elements can hence
act as either an oxidant or a reductant as seen in the Hydrogen module.
The
elemental form (and other intermediate oxidation states) may react by
autooxidation-reduction as seen in the examples below.
In these reactions an atom in an intermediate oxidation state acts as both the oxidant and the reductant.
The conditions under which autooxidation-reduction takes place varies from system to system.
| 3NO2(g) | + | H2O |  | 2HNO3(l) | + | NO(g)3 | | 4KClO3(s) |  | 3KClO4(s) | + | KCl(s) |
| N(+4) | | | | N(+5) | | N(+2) | | Cl(+5) | | Cl(+7) | | Cl(-1) |