Write balanced chemical equation for the following reactions:

Dichlorine heptaoxide $\left({\mathrm{Cl}}_2{\mathrm{O}}_7\right)$ in gaseous state combines with an aqueous solution of hydrogen peroxide in acidic medium to give chlorite ion $\left({\mathrm{ClO}}_2^{-}\right)$ and oxygen gas.

(Balance by ion electron method)

Calculate the oxidation number of phosphorus in the following species.

${\mathrm{HPO}}_3^{2-}$

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.

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

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