I know from all my textbooks books that $SO_4$ has a -2 charge I.e S=+6 and O=-8 charge. My Q is how did we find it and solve it . Like for every Q I solve . For example , KMnO_4. K= +1. O=-8. So , to find for Mn we equate all the charges to 0. So , Mn=+7. But why not the same case for SO4?
@JohnRennie Hi I forgot to wish you on your birthday :-( You were not online when I wanted to wish you, then it slipped out of my mind, and today, which is pretty late, I realise..... Happy belated birthday
@Sarabsrimt $\mathrm{Na}^+$ is a monoatomic ion while $\mathrm{SO}_4$ is a polyatomic ion. Sodium ion is formed by donating 1 electron so it is stable and the polyatomic ion is complex and I don't have knowledge about it.