' X ' is the number of electrons in t_2 g orbitals of the most stable complex ion among [ Fe ( NH_3)_6]^3+,[ FeCl_6]^3-,[ Fe ( C_2 O_4)_3]^3- and […

' X ' is the number of electrons in $\displaystyle \mathrm{t}_{2 \mathrm{~g}}$ orbitals of the most stable complex ion among $\displaystyle \left[\mathrm{Fe}\left(\mathrm{NH}_3\right)_6\right]^{3+},\left[\mathrm{FeCl}_6\right]^{3-},\left[\mathrm{Fe}\left(\mathrm{C}_2 \mathrm{O}_4\right)_3\right]^{3-}$ and $\displaystyle \left[\mathrm{Fe}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{3+}$. The nature of oxide of vanadium of the type $\displaystyle \mathrm{V}_2 \mathrm{O}_{\mathrm{X}}$ is :