Below are drawn four possible isomers $($partial Lewis structures with different atomic connectivity$)$ for an anion with the molecular formula $C_3{H}_{4}N{O}^{-}2e^{-}$

A

B

C

D

$($a$)$ First, add enough electrons as either lone pairs or $$ bonds to give an overall negative charge.

Show all lone pairs in each completed Lewis structure, and show any atomic formal charges that result.

$($b$)$ Then, for each isomer, consider if other resonance structures can contribute. Since this is an anion, look for a strong electron donor with an adjacent electron acceptor. For each additional resonance structure you draw $($some isomers may have more than one additional RS$,$ some may have none$),$ circle the electron pairs in the original Lewis structure which have moved, and draw a curved arrow depicting the motion required to create the new RS$.$ If you have colored pens, color coding your electrons pairs is nice $($but not required$).$