Which of the following show electromeric effect?

The complete transfer of the shared pair of pi-electrons of a multiple bond to one of the atoms in the presence of the attacking agent is called electromeric effect. It is a temporary effect and observed only in organic compounds with multiplebonds in the presence of attacking reagent. It come into play instantaneously at the demand of the
attacking reagent and when it is removed, the original condition is restored. Electron rich/deficient reagent is needed.