Calculate formal charge (F) on nitrogen and Oxygen atoms marked 'a' and 'b' in the following Lewis structure of `NHO_(3),`

Explanation

Formal charge on N atom `= V - S/2 -U=5 - 8/2 -0=+1`
Formal charge on O atom `= V - S/2 - U=6 - 2/2 -6 =-1`
On this basis lewis structure of `HNO_(3)` may also be written as shown below:

It should be noted that formal charges do not indicate real charge sparation within the molecule, but indication of the formal charges on the atoms in the Lewis structure only helps in keeping track of the valence electrons in the molecule.