The  $I_1,I_2,I_3,I_4$ values of an element ‘M’ are 120, 600, 1000 , and 8000 kJ/mole respectively then the formula of its sulphate.

Due to attainment of stable configuration after losing 3 electrons, there is sudden increase in  I4 from I3, hence it has 3 electrons in the valence shell.${\mathrm{M}}^{+3}{\left({\mathrm{SO}}_4\right)}^{-2}\to M_2{\left({\mathrm{SO}}_4\right)}_3$