' X ' is the number of electrons in t_ 2 g orbitals of the most...

' $X$ ' is the number of electrons in $t_{2 g}$ orbitals of the most stable complex ion among \left[\mathrm{Fe}\left(\mathrm{NH}_3\right)_6\right]^{3+}, \left[\mathrm{Fe}\left(\mathrm{Cl}_6\right)\right]^{3-},\left[\mathrm{Fe}\left(\mathrm{C}_2 \mathrm{O}_4\right)_3\right]^{3-} and $\left[\mathrm{Fe}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{3+}$. The nature of oxide of vanadium of the type $\mathrm{V}_2 \mathrm{O}_{\mathrm{X}}$ is: