Chemistry and Chemical Reactivity (9th Edition)

Nitrogen is in group 15, having 5 valence electrons, oxygen and sulfur are in group 16, carbon in 14. $O_3: 3×6=18$ $OCN^-: 6+4+5+1=16$ $NO_2^-: 5+2×6+1=18$ $SO_2: 6+6×2=18$