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.

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

Identify the redox reactions out of the following reactions and identify the oxidising and reducing agents in them.

$3\mathrm{HCl}\left(\mathrm{aq}\right)+{\mathrm{HNO}}_3\left(\mathrm{aq}\right)\to {\mathrm{Cl}}_2\left(\mathrm{g}\right)+\mathrm{NOCl}\left(\mathrm{g}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$

Identify the redox reactions out of the following reaction and identify the oxidising and reducing agents in them.

${\mathrm{HgCl}}_2\left(\mathrm{aq}\right)+2\mathrm{KI}\left(\mathrm{aq}\right)\to {\mathrm{Hgl}}_2\left(\mathrm{s}\right)+2\mathrm{KCl}\left(\mathrm{aq}\right)$

Identify the redox reactions out of the following reactions and identify the oxidising and reducing agents in them.

${\mathrm{Fe}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)+3\mathrm{CO}\left(\mathrm{g}\right)\stackrel{∆}{\to }2\mathrm{Fe}\left(\mathrm{s}\right)+3{\mathrm{CO}}_2\left(\mathrm{g}\right)$

Identify the redox reactions out of the following reactions and identify the oxidising and reducing agents in them.

${\mathrm{PCl}}_3\left(\mathrm{l}\right)+3{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to 3\mathrm{HCl}\left(\mathrm{aq}\right)+{\mathrm{H}}_3{\mathrm{PO}}_3\left(\mathrm{aq}\right)$