In the reaction; ${\mathrm{As}}_2{\mathrm{S}}_3+{\mathrm{HNO}}_3⟶{\mathrm{H}}_3{\mathrm{AsO}}_4+{\mathrm{H}}_2{\mathrm{SO}}_4+\mathrm{NO}$ the element(s) oxidized is/are:

As₂​S₃​ + HNO₃​ → H₃​AsO₄​ + H₂​SO₄​ + NO

+3  -2         +5           +5           +6          +2
                            (oxidation) (oxidation)(reduction)
Hence, the elements oxidized are both As and S.

$\begin{array}{c}{\mathrm{As}}^{3+}⟶{\mathrm{As}}^{5+}+2{\mathrm{e}}^{-}\\ {\mathrm{S}}^{2-}⟶{\mathrm{S}}^{6+}+8{\mathrm{e}}^{-}\end{array}$