Final answer:
Resonance forms are used to describe the distribution of electrons in molecules or ions. Pairs B and C are reasonable resonance forms among the given options.
Step-by-step explanation:
Resonance forms describe the distribution of electrons in molecules or ions. In the given options, pairs B (N+ - O-) and C (C+ - N-) are reasonable resonance forms. Resonance occurs when there are multiple valid Lewis structures that can be drawn for a molecule or ion to accurately represent its electronic structure. The distribution of electrons in resonance forms helps to explain the stability and reactivity of compounds.