Which reagent must be added to the reaction along with phenyl magnesium bromide to produce 2-phenyl ethanol?

The correct answer is option 4.

The name of the compound is ethylene oxide.  The reagent that must be added to the reaction along with phenylmagnesium bromide \((PhMgBr)\) to produce 2-phenyl ethanol is ethylene oxide \((C_2H_4O)\).

Phenylmagnesium bromide \((PhMgBr)\) is a Grignard reagent, a nucleophilic species commonly used for carbon-carbon bond formation.

Ethylene oxide is a cyclic ether, containing a three-membered ring with an oxygen atom.

The reaction between these two components involves nucleophilic attack by the Grignard reagent on the electrophilic carbon atom in the ethylene oxide ring. This breaks the \(C-O\) bond in the epoxide ring and forms a new carbon-carbon bond between the phenyl group \((Ph)\) from \(PhMgBr\) and the carbon atom that was originally bonded to the oxygen in the epoxide.

When the reaction mixture is quenched with water \((H_2O)\) or dilute acid, the magnesium-oxygen bond is cleaved, and the final product, 2-phenyl ethanol \((PhCH_2CH_2OH)\), is obtained.

Here is the summarized reaction: