Final answer:
The nitrite ion (NO2-) has two valid resonance structures. These structures reflect different possible arrangements of a double bond within the ion, and the true structure is a hybrid of these two resonance structures.
Step-by-step explanation:
The student has asked to predict the number of resonance structures for a nitrite ion, NO2-. In chemistry, resonance structures represent different ways to draw the same molecule, showing different possible configurations of double bonds and lone pairs while the arrangement of atoms remains the same.
For the nitrite ion (NO2-), there are two valid resonance structures. These structures are distinguished by the location of the double bond. In one structure, the double bond is between one of the oxygen atoms and the nitrogen, while the other oxygen atom has a single bond with the nitrogen and carries a negative charge. The second structure has these positions reversed.
Experimentally, it is observed that both N-O bonds in the nitrite ion are the same length and strength, which supports the resonance theory. This means that neither resonance structure is 'correct' in the classical sense; instead, the true structure is a hybrid of both resonance structures.