Question

In nitrate ion what should be total of Formal Charge on each atom? Why?

Answer 1

The formal charge of the nitrate anion is of course - 1. In the Lewis representation at least 3 of the four participating atoms bear a formal charge

For N, we are counting 4 electrons (4 bonding electrons, no nonbonding electrons). Since N is in Group VA, we have one less electron than N should have, and so it has a +1 charge. As a check, your formal charges should add up to the charge of the atom (-1 for nitrate).