In the following electron-dot structure, calculate the formal charge on each nitrogen atom from left to right  $\left[\underset{..}{\overset{..}{\mathrm{N}}}=\mathrm{N}=\underset{..}{\overset{..}{\mathrm{N}}}\right]$

$\underset{..}{\overset{..}{\mathrm{N}}}=\mathrm{N}=\underset{..}{\overset{..}{\mathrm{N}}}$
[F.C]_1N = 5 - 1/2 x 4 - 4
           = 5-6 = -1
[F.C]_2N = 5 - 1/2 x 8 - 0
           = 5-4 = +1
[F.C]_3N = 5 - 1/2 x 4-4
           = 5-2-4 = -1