Which of the following represents a valid pair of resonance structures?

Step-by-step solution

Resonance structures must have the identical arrangement of atoms. Only the placement of electrons and non-bonding electrons can differ. In option (A), the electrons of the double bond move to the adjacent carbon-carbon single bond, shifting the positive charge to the other end of the allylic system. The positions of all atoms, including hydrogens, remain exactly the same. This represents a valid allylic resonance pair. In option (B), the terminal group changes from =CH₂ in the first structure to -CH₃ in the second