The most stable oxidized species among the following is: 
\(E_{{\mathrm{Cr}_2 \mathrm{O}_7^2}/ \mathrm{Cr}^{3+}}^{o} =1.33 \mathrm{~V} ; E_{\mathrm{Cl}_2 / \mathrm{Cl}^{-}}^{o}=1.36 \mathrm{~V} \)
\( E_{\mathrm{MnO_{4}}^{-} / \mathrm{Mn}^{2+}}^{o}=1.51 \mathrm{~V} ; E_{\mathrm{Cr}^{3+} / \mathrm{Cr}}^{o}=-0.74 \mathrm{~V}\)

1. Cr3+  2. MnO4-
3. Cr2O72- 4. Mn2+ 
HINT: Lower the value of reduction potential, the higher will be the stability of oxidized species.
Explanation:
E°Cr3+/Cr has most - ve value equal to -0.74 among the given four choices. So, Cr3+ is the most stable oxidized species.