${\mathrm{HNO}}_3$ oxidises ${\mathrm{NH}}_4^{+}$ ions to nitrogen and itself gets reduced to ${\mathrm{NO}}_2$. The moles of ${\mathrm{HNO}}_3$ required by 1 mole of $({\mathrm{NH}}_4{)}_2{\mathrm{SO}}_4$ is :

The complete reaction with oxidation number is given as,

${\mathrm{HNO}}_3^{+5}+2{\mathrm{NH}}_4^{+}⟶{\mathrm{N}}_2^0+{\mathrm{NO}}_2^{+4}$

$n\cdot f=1 n\mathit{.}f=6$

$n\times 1=1\times 6$

$n=6$.

Thus, the correct option is C.