Question

S-->SO3-->H2SO4-->H2O-->BaSO4

Answer 1

1)2S+3O2=2SO3
2)SO3+H2O=H2SO4
3)H2SO4+Mg(OH)2=MgSO4+2H2O
4)MgSO4+Ba(OH)2=BaSO4+Mg(OH)2