Explain why ${\mathrm{HNO}}_3$ acts only as an oxidising agent while ${\mathrm{HNO}}_2$ can act both as a reducing agent and as an oxidising agent?

In which of the following compounds, sulphur has the highest oxidation state?

${\mathrm{SO}}_2, {\mathrm{H}}_2{\mathrm{SO}}_4, {\mathrm{Na}}_2{\mathrm{S}}_2{\mathrm{O}}_3 \mathrm{and} {\mathrm{Na}}_2{\mathrm{S}}_4{\mathrm{O}}_6$.

Calculate oxidation state of nitrogen in each of the following compounds.

${\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_5\mathrm{Cl}\right]}^{2+}, {\mathrm{NH}}_4\mathrm{OH}, {\left({\mathrm{N}}_2{\mathrm{H}}_5\right)}_2{\mathrm{SO}}_4 \mathrm{and} {\mathrm{Mg}}_3{\mathrm{N}}_2$.