The correct options are
B D Electromeric effect is an temporary effect, it is observed only in presence of attacking reagent. This involves the shifting of
π in the mutiple bond.
When the
πelectrons of the multiple bond are transferred to the atom to which the reagent gets attached, it is called positive electromeric effect (+E).
When the
πelectrons of the multiple bond are transferred to the atom to which the reagent does not get attached, it is called negative electromeric effect (-E).
In (a) and (c), the
πelectrons of the double bond is transferred to
H+and Br+. Hence, these reaction shows +E effect.
In (b) and (d), the
πelectrons of the double bond is transferred to oxygen atom which is not the attacking reagent here. So (b) and (d) show -E effect.
Therefore, answer is option (b) and (d).