Balance the following half-reactions, which take place in acidic solution.

c. $\mathrm{NO}_3{ }^{-}(aq) \rightarrow \mathrm{HNO}_2(aq)$

NO$_3^-$(aq) $\rightarrow$ HNO$_2$(aq)

In order to balance an oxidation-reduction reaction or half reaction, the mass as well as the charge need to be balanced.