Strongest oxidising power among the option is Mn2O3 because of E∘ value $\begin{aligned}
& \mathrm{E}_{\mathrm{Mn}^{+3} / \mathrm{Mn}^{+2}}^{\circ}=+1.57 \mathrm{V} \
& \mathrm{Mn}^{+3} \rightarrow \mathrm{d}^4 \text { configuration } \
& \mu=\sqrt{24} \mathrm{BM} \
& =4.89 \mathrm{BM} \
& \Rightarrow 5
\end{aligned}$