The formal charges on the atoms marked as (1) to (4) in the Lewis...

The formal charge (F.C.) of an atom in a Lewis structure is calculated using the formula:
F.C. = [Total valence electrons] - [Total non-bonding (lone pair) electrons] - $\frac{1}{2}$[Total bonding (shared) electrons]
For atom (1) Oxygen: Valence $e^- = 6$, Lone pair $e^- = 4$, Bonding $e^- = 4$.
$F.C. = 6 - 4 - \frac{1}{2}(4) = 0$
For atom (2) Nitrogen: Valence $e^- = 5$, Lone pair $e^- = 0$, Bonding $e^- = 8$.
$F.C. = 5 - 0 - \frac{1}{2}(8) = +1$
For atom (3) Oxygen: Valence $e^- = 6$, Lone pair $e^- = 4$, Bonding $e^- = 4$.
$F.C. = 6 - 4 - \frac{1}{2}(4) = 0$
For atom (4) Oxygen: Valence $e^- = 6$, Lone pair $e^- = 6$, Bonding $e^- = 2$.
$F.C. = 6 - 6 - \frac{1}{2}(2) = -1$
The formal charges are $0, +1, 0, -1$ respectively.