Which forms interstitial compounds?

The metal with the highest oxidation state present in $K_2CrO_4$,$NbCl_5$,and $MnO_2$ is

Given below are two statements:
Statement $I$: Ferromagnetism is considered as an extreme form of paramagnetism.
Statement $II$: The number of unpaired electrons in a $Cr^{2+}$ ion $(Z=24)$ is the same as that of a $Nd^{3+}$ ion $(Z=60)$.
In the light of the above statements,choose the correct answer from the options given below:

Based on the given outer electronic configurations,which element will exhibit the highest oxidation state?

Why are the $E^o$ values for $Mn^{2+}/Mn$,$Zn^{2+}/Zn$,and $Ni^{2+}/Ni$ more negative than expected? The table below provides the values:
| $E^o_{Mn^{2+}/Mn}$ | $E^o_{Zn^{2+}/Zn}$ | $E^o_{Ni^{2+}/Ni}$ |
| :--- | :--- | :--- |
| $-1.18 \ V$ | $-0.76 \ V$ | $-0.25 \ V$ |

For the four consecutive transition elements $Cr, Mn, Fe,$ and $Co$,the correct order of stability of their $+2$ oxidation state is: