Which one of the following exhibits the largest number of oxidation states?

Here Mn $\left(3{\mathrm{d}}^{5}4{\mathrm{s}}^2\right)$  exhibits the largest number of oxidation state.

Manganese exhibit the largest number of oxidation states. It shows the oxidation states +2, +3, +4, +5 ,+6, and + 7. The reason for that is the maximum number of unpaired electrons present in its outermost shell i.e. $3d^{5}4s^2$