Which species have delocalized \(\pi \) electrons?

I.     \({\text{C}}{{\text{H}}_{\text{3}}}{\text{COC}}{{\text{H}}_{\text{3}}}\)

II.     \({\text{NO}}_{\text{2}}^ - \)

III.     \({\text{CO}}_{\text{3}}^{2 - }\)

A.     I and II only

B.     I and III only

C.     II and III only

D.     I, II and III

C

Although 70% of the candidates gave the expected answer, C, there is minimal delocalization in ethanoic acid, so both C and D were accepted (giving an 86% success rate on the question).