How many of the following are with highest oxidation number for its central atom? ${\mathrm{H}}_2{\mathrm{SO}}_4,{\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_8,{\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_7,{\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7,{\mathrm{H}}_4{\mathrm{XeO}}_6,{\left({\mathrm{NH}}_4\right)}_3{\mathrm{PO}}_4,{\mathrm{Mg}}_2{\mathrm{P}}_2{\mathrm{O}}_7,{\mathrm{SO}}_3^{-2},\mathrm{FeO}$

Oxidation state of S in H₂SO₄, H₂S₂O₇ and H₂S₂O₈ is the same, +6. Oxidation number of Cr in K₂Cr₂O₇ is +6. Oxidation number of Xe in H₄XeO₆ is +8. Oxidation state of P in ${\left({\mathrm{NH}}_4\right)}_3{\mathrm{PO}}_4 \mathrm{and} {\mathrm{Mg}}_2{\mathrm{P}}_2{\mathrm{O}}_7$ is the same, +5.