Final answer:
The correct resonance structures for the nitrite ion, NO2-, are depicted in Option 2: Resonance structure 1, 2, and 3, showing various electron distributions between nitrogen and oxygen atoms.
Step-by-step explanation:
The resonance structures for a nitrite ion, NO2−, represent different possible structures that describe the distribution of electrons within the ion. Resonance structures are a way to illustrate the delocalization of electrons, particularly in ions like nitrite where the electrons are not localized between just one set of atoms. In the nitrite ion, there are indeed two resonance structures, each showing a different arrangement of a single and a double bond to the nitrogen atom. However, experimental evidence shows that both nitrogen-oxygen bonds in the nitrite ion are equivalent, indicating that the true structure is an average of the resonance forms.
Therefore, the correct answer to the question, 'Which of the following are resonance structures for a nitrite ion, NO2−?' is Option 2: Resonance structure 1, 2, and 3. These three resonance structures depict the two states where one oxygen has a double bond and the other has a single bond along with the radical structure.