Which of the species below will exhibit resonance? co2, co3 2−, no3 −, o3?

Resonance, also called as Mesomerism explains the position of those electrons which are not localized and their position can't be explained by a simple single Lewis structure. In resonance the position of Nuclei remains same while that of delocalized electrons changes.

As asked, all the given molecules and polyatomic ion show the phenomenon of resonance. Their contributing structures or canonical forms are shown below, structures are in following order,
1) CO₂
2) CO₃²⁻
3) NO₃⁻
4) O₃

Ibelieve your answer is true 

Ithink is a because if say increased in electronegativity