Q. Assertion: Electromeric effect is brought into play only at the requirement of the reagent.
Reason: It is a temporary effect in which bond pair is shifted to one of the constituent atoms.

 2496  242 AIIMSAIIMS 2009Organic Chemistry – Some Basic Principles and Techniques Report Error

Solution:

It is a temporary effect. It comes into play instantaneously at the demand of the attacking reagent and as soon as the attacking reagent is removed the original condition is restored.

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This effect is applicable on a multiple bond.