Final answer:
Resonance in nitrate refers to the multiple ways of depicting the arrangement of electrons in the ion. Nitrate has three resonance structures, but the actual structure is an average or hybrid of these structures. The extra electrons are not shared between all three bonds simultaneously, and the distribution of electrons in nitrate does not switch between different resonance structures. Most of the nitrate ions exist in the stable average form, while the other two forms may be observed rarely.
Step-by-step explanation:
Resonance in the context of nitrate means that there are multiple ways to depict the arrangement of electrons in the ion. Nitrate (NO3-) has three resonance structures, which are different ways of arranging the bonds and electrons. The actual structure of nitrate is an average or hybrid of these three resonance structures. This means that the extra electrons in nitrate are not shared between all three bonds all at the same time (option A), nor is nitrate found in nature with one-third of the ions having one resonance structure, one-third with another, and one-third with another (option B). Instead, the actual structure of nitrate is an average of the three resonance structures, and it does not switch between the different resonance structures (option C). Most of the nitrate ions will exist in the most stable form, which is the average or hybrid of the three resonance structures, and the other two forms may be observed on rare occasions (option D).