Calculate the oxidation number of phosphorus in the following species.

${\mathrm{PO}}_4^{3-}$

Calculate the oxidation number of each sulphur atom in the following compound:

${\mathrm{Na}}_2{\mathrm{S}}_2{\mathrm{O}}_3$

Calculate the oxidation number of each sulphur atom in the following compounds:

${\mathrm{Na}}_2{\mathrm{S}}_4{\mathrm{O}}_6$

Calculate the oxidation number of each sulphur atom in the following compound:

${\mathrm{Na}}_2{\mathrm{SO}}_3$

Calculate the oxidation number of each sulphur atom in the following compound:

${\mathrm{Na}}_2{\mathrm{SO}}_4$

Balance the following equation by the oxidation number method.

${\mathrm{Fe}}^{2+}+{\mathrm{H}}^{+}+{\mathrm{Cr}}_2{{\mathrm{O}}_7}^{2-}\to {\mathrm{Cr}}^{3+}+{\mathrm{Fe}}^{3+}+{\mathrm{H}}_2\mathrm{O}$

${\mathrm{I}}_2+{{\mathrm{NO}}_3}^{-}\to {\mathrm{NO}}_2+{{\mathrm{IO}}_3}^{-}$

Balance the following equation by the oxidation number method.

${\mathrm{I}}_2+{\mathrm{S}}_2{{\mathrm{O}}_3}^{2-}\to {\mathrm{I}}^{-}+{\mathrm{S}}_4{{\mathrm{O}}_6}^{2-}$

Balance the following equation by the oxidation number method.

${\mathrm{MnO}}_2+{\mathrm{C}}_2{{\mathrm{O}}_4}^{2-}\to {\mathrm{Mn}}^{2+}+{\mathrm{CO}}_2$