Among the following, which is the strongest oxidizing agent?

The substance which will have the highest value of reduction potential will be the strongest oxidising agent. The values of reduction potential are as follow

$\begin{array}{r}{\mathrm{E}}_{{\mathrm{Mn}}^{3+}/{\mathrm{Mn}}^{2+}}^0=+1.57\mathrm{V}\\ \\ {\mathrm{E}}_{{\mathrm{Ti}}^{3+}/{\mathrm{Ti}}^{2+}}^0=-0.37\mathrm{V}\\ \\ {\mathrm{E}}_{{\mathrm{Fe}}^{3+}/{\mathrm{Fe}}^{2+}}^0=+0.77\mathrm{V}\\ \\ {\mathrm{E}}_{{\mathrm{Cr}}^{3+}/{\mathrm{Cr}}^{2+}}^0=-0.41\mathrm{V}\end{array}$

As we can see ${\mathrm{Mn}}^{+3}$ has the highest value of standard reduction potential, so it will be the strongest oxidising agent.