a. Draw resonance contributors for the following species, showing all the lone pairs:
b. For each species, indicate the most stable resonance contributor.
3. NO₂^-

Resonance structures are different Lewis structures for the same molecule that depict the same arrangement of atoms but differ in the distribution of electrons. These structures help illustrate the delocalization of electrons within a molecule, which can stabilize the overall structure. In the case of NO2-, resonance contributors can be drawn to show how the negative charge and lone pairs can be distributed across the nitrogen and oxygen atoms.

Lone pairs are pairs of valence electrons that are not involved in bonding and are localized on a specific atom. In resonance structures, it is crucial to accurately represent lone pairs, as they can influence the molecule's reactivity and stability. For NO2-, the placement of lone pairs on the nitrogen and oxygen atoms will affect the resonance contributors and the overall charge distribution.

The stability of resonance contributors is determined by factors such as the octet rule, formal charges, and the electronegativity of atoms. More stable resonance structures typically have a complete octet for all atoms, minimized formal charges, and negative charges on more electronegative atoms. Identifying the most stable resonance contributor for NO2- involves evaluating these factors to determine which structure best represents the molecule's electron distribution.