The resonating structures are as follow:-
Cl atom has loan pair and the loan pair of electrons are in conjugation with the double bond, hence the molecule shows resonance.
The two double bonds are at alternate position, hence, the condition of conjugation is satisfied and the resonance is possible in the molecule.
The two double bond are again in conjugation, as present at alternate position, and as the negative charge is more stable at O, as Oxygen atom is more electronegative atom, hence the structure Iis more stable.
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