The task is to add the missing particles ([tex]H_3O,OH,H_2O[/tex]) and balance . (1) is a basic solution while (2) and (3) are acidic. [tex]MnO_4 + SO_3 \rightarrow MnO_4 + SO_4[/tex] [tex]Zn + NO_3 \rightarrow Zn + N_2O[/tex] [tex]Au + NO_3 + Cl \rightarrow AuCl_4 + NO[/tex] I think that they should all have [tex]H_2O[/tex] on the left side but only the first one has [tex]OH[/tex] on the right side, while the other two, that are acidic have [tex]H_3O[/tex] on the right side? And after that, it's just pure balancing. The biggest concern is pretty much to place the ions and the water molecule (if any) on the correct spot.