From the list of  ${\mathrm{H}}_2{\mathrm{SO}}_4,{\mathrm{SO}}_2,{\mathrm{H}}_2{\mathrm{SO}}_3,{\mathrm{H}}_2\mathrm{S}, {\mathrm{HNO}}_2$

How many can  act like both oxidant and reductant

$\stackrel{+4}{\mathrm{S}}{\mathrm{O}}_2,{\mathrm{H}}_2\stackrel{+4}{\mathrm{S}}{\mathrm{O}}_3.$   Sulphur in these compounds is in intermediate oxidation state (between +6 and –2). They can undergo both oxidation and reduction. Nitrous acid also due to the fact that its oxidation state is +3, it can accept as well as release electrons.