Redox Reactions

Among the given options, oxidation state of

sulphur in $\mathrm{SO}_3^{-2}=+4$

carbon in $\mathrm{CO}_3^{-2}=+4$

sulphur in $\mathrm{SO}_4^{-2}=+6$

nitrogen in $\mathrm{NO}_3^{-}=+5$

Since, $\mathrm{K}_2 \mathrm{Cr}_2 \mathrm{O}_7$ is a strong oxidising agent it can oxidise the species, which is not in its most possible positive oxidising state.

Thus, $\mathrm{SO}_3^{-2}$ can react with $\mathrm{K}_2 \mathrm{Cr}_2 \mathrm{O}_7$ as follows:

$\mathrm{Cr}_2 \mathrm{O}_7^{2-}(a q)+3 \mathrm{SO}_3^{2-}(a q)+8 \mathrm{H}^{+}(a q) \longrightarrow 2 \mathrm{Cr}^{3+}(a q)+3 \mathrm{SO}_4^{2-}(a q)+4 \mathrm{H}_2 \mathrm{O}(l)$