Find the number of compound which has four orbitals participating in bybridisation in central atom.

(a) ${\mathrm{K}}_2{\mathrm{CrO}}_4$    (b) ${\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7$

(c)  ${\mathrm{KMnO}}_4$      (d) ${\mathrm{K}}_2{\mathrm{MnO}}_4$

(e) ${\left[\mathrm{Ni}(\mathrm{CN}{)}_4\right]}^{2-}$     (f) $\left[{\mathrm{NiCl}}_4{\mathrm{I}}^{2-}\right.$

(g) ${\left[{\mathrm{PtCl}}_4\right]}^{2-}$     (h) ${\mathrm{Na}}_4{\mathrm{P}}_2{\mathrm{O}}_7$

(i) ${\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_8$