Which specie contains only covalent bonds?

The species contains only covalent bonds is sulphuric acid(${\mathrm{H}}_2{\mathrm{SO}}_4$)

The parent ions of potassium dichromate, aluminium fluoride, and ammonium nitrate are simple to determine from the formulas. ${\mathrm{Al}}^{3+};{\mathrm{Al}}^{3+},3\times {\mathrm{F}}^{-};{\mathrm{NH}}_4^{+},{\mathrm{NO}}_3^{-};2\times {\mathrm{K}}^{+},{\mathrm{Cr}}_2{\mathrm{O}}_7^{2-}$

The optimal response is c because sulfuric acid, on the other hand, is the hydrate of a non-metal oxide called an oxyacid.