${{\text{n}}^{\text{2}}}{\text{  +  2n  -  4}}{\text{.9  =  0  }}\therefore {\text{ n  =  4}}$

${\text{M}}{{\text{n}}^{\text{3}}}{\text{ +  [Ar] 3}}{{\text{d}}^{\text{4}}}$ $\therefore {\text{ }}$ સંયોજન ${\text{M}}{{\text{n}}_{\text{2}}}{{\text{O}}_{\text{3}}}$