The formal charge of nitrogen in the compound NO3 is plus 1. The whole nitrate ion carries a total charge of minus 1 when combining the charges of the one nitrogen atom and three oxygen atoms.
The formal charge is found by subtracting the number of lone electrons and half the number of bonded electrons from the total number of valence electrons. The nitrogen atom has no lone electrons, four bonding electrons and five valence electrons. The charge is found through the formula 5 - 4 - 0 = 1. In the ion, two of the oxygen atoms have a formal charge of minus 1.