Write the reaction equations: SO2 → SO3 → X → BaSO4

SO2 can be further oxidized with oxygen to SO3, do not forget to put down coefficients for equilibrium.
2SO2 + O2 → 2SO3;
SO3 is an acidic oxide that can react with water to form acid.
SO3 + H2O → H2SO4;
A quality reagent for sulfate ion will be soluble barium salts (BaCl2) resulting in a white precipitate (BaSO4).
Н2SO4 + BaCl2 → BaSO4 + 2HCl.

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