A typical (if outdated) Lewis structure of sulfuric acid is:
(HO−)2S(=O)2
This Lewis structure is equivalent to:
(HO−)2S2+(−O−)2
For a neutral chalcogen atom (chalcogen = S or O), there must be 6 valence electrons. In the representation (HO−)2S(=O)2 there are certainly 6 electrons associated with each sulfur or oxygen. Lone pairs are owned by the atom, and thus on neutral oxygen there are 2 electrons from the double bond, and 4 electrons in the lone pairs).
Now of course both H2SO4 and HSO−4 are strong acids, and undergoes almost complete ionization in water:
H2SO4(aq)+2H2O(l)→SO2−4+2H3O+
Conservation of charge demands that the sulfate ion has 2 formal negative charges.
Nitric acid has an even more problematic representation: (O=)N+(−O−)(−OH), where there is formal charge separation in even the neutral acid (6 electrons around nitrogen rather than 7; 9 electrons around oxygen rather than 8 ).
See here for another example that assigns formal charge.
