The Gattermann-Koch reaction is used in the industrial preparation of Benzaldehyde. The electrophile involved in this reaction is</p

\(HCO^+\)

The correct answer is option 3. \(HCO^+\).

The Gattermann-Koch reaction is a chemical reaction used for formylation of aromatic rings, such as in the industrial preparation of benzaldehyde from benzene. This reaction involves the introduction of a formyl group (\(-CHO\)) onto the benzene ring using carbon monoxide and hydrochloric acid in the presence of a Lewis acid catalyst, typically aluminum chloride \((AlCl_3)\) or cuprous chloride \((CuCl)\).

The electrophile generated in the Gattermann-Koch reaction is the formyl cation (\(HCO^+\)). This formyl cation is produced from the reaction of carbon monoxide (CO) and hydrochloric acid (HCl) in the presence of the Lewis acid catalyst.

The mechanism of the reaction will be as follows:

This formyl cation is the active electrophile that facilitates the formylation of the benzene ring to produce benzaldehyde in the Gattermann-Koch reaction.