Final answer:
The carbon atom in the carbonyl group (C=O) is the electrophilic site due to its partial positive charge, making it susceptible to attack by nucleophiles.
Step-by-step explanation:
The electrophilic site in a molecule is the location where an electrophile has a positive charge or is positively polarized, making it susceptible to attack by a nucleophile. In the context of the molecule C=O, oxygen (O) is more electronegative than carbon (C), which results in a distribution of charge where oxygen carries a partial negative charge (8−) and carbon carries a partial positive charge (8+). This makes the carbon atom of the carbonyl group the electrophilic site because it has a deficiency of electrons and can attract electron-rich species, such as nucleophiles. The oxygen, being more electronegative, is not electrophilic but rather nucleophilic. Therefore, for the molecule presented, the carbon atom (option 1) is the electrophilic site within the carbonyl group.