Would either hno2 or no−2 be expected to exhibit resonance?

                 Both HNO₂ and NO₂⁻ can exhibit resonance but, it is more prominent in NO₂⁻ ion.

                          Resonance is the method of explaining delocalized electrons in a molecule or polyatomic ion where the structure is not possible to be explained ba single Lewis structure.

                           Below figure shows the resonance of both HNO₂ and NO₂⁻. The resonance in HNO₂ is less prominent because a positive charge forms in one of the corresponding forms which makes it highly unfavorable. While, in case of NO₂⁻ a negative charge is present on oxygen atom in both cases which is favorable.

in chemistry, a solution’s concentration is how much of a dissolvable substance, known as a solute, is mixed with another substance, called the solvent. the standard formula is c = m/v, where c is the concentration, m is the mass of the solute dissolved, and v is the total volume