The number of d- electrons in ${\mathrm{Mn}}^{2+}$ is equal to that of :

$m_n^{2+}\Rightarrow \left[Ar\right]3d^5$

No. of  $\mathrm{d}-{\mathrm{e}}^{-}=5$.

Now s-electrons in Na,

$N_7\to {\text{ 1s}}^{2}2s^{2}2p^3$

d-electrons in ${\mathrm{Fe}}^{+3}$,

${\text{ Na }}_{11}\to 1s^{2}2s^{2}2p^{6}3s^1$.