After the electrons have been assigned according to the vertical red lines on the formula, the total number of valence electrons that now "belong" to each atom is subtracted from the number of valence electrons of the neutral atom (such as 5 for nitrogen in group 15) to yield that atom's oxidation state.
after the electrons have been assigned according to the vertical red lines on the formula the total number of valence electrons that now "belong" to each atom is subtracted from the number of valence electrons of the neutral atom (such as 5 for nitrogen in group 15) to yield that atom's oxidation state