Electromeric effect is a temporary effect. Assign reason.

Explanation

**Step-by-Step Text Solution:**

1. **Definition of Electromeric Effect:** The electromeric effect refers to the temporary shift of electrons in a molecule due to the influence of an attacking reagent, such as a nucleophile or electrophile. This effect is primarily observed in compounds with multiple bonds, such as alkenes (double bonds) and alkynes (triple bonds), as well as in carbonyl compounds (like aldehydes and ketones).

2. **Presence of Multiple Bonds:** The electromeric effect occurs in species that have multiple bonds. For example, consider a carbonyl group (C=O). In the absence of any attacking reagent, the electrons in the double bond remain localized and do not move.

3. **Role of the Attacking Reagent:** The key reason the electromeric effect is temporary is that it only occurs in the presence of an attacking reagent. When a nucleophile approaches the carbonyl group, the pi bond (C=C or C=O) can break, leading to a heterolytic cleavage. This process results in the formation of a negative charge on the more electronegative atom (like oxygen in the case of carbonyls) and allows the nucleophile to attack.

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