Explain the difference between valence and oxidation number.

Starting with the correctly balanced half-reactions, write the overall net ionic reaction for the following:
Chloride ion is oxidised to ${\mathrm{Cl}}_2$ by $\underline{\mathrm{Mn}}{\mathrm{O}}_4^{-}$ ( in acid solution). Also, find out the change in the oxidation number of the underlined atom.

Starting with the correctly balanced half-reactions, write the overall net ionic reaction for the following change:

Nitrous acid $\left(\mathrm{H}\underline{\mathrm{N}}{\mathrm{O}}_2\right)$ reduces ${{\mathrm{MnO}}_4}^{-}$( in acid solution). Also, find out the change in the oxidation number of the underlined atom.