Identify the reagent required to carry out the following transformation:

Step-by-step solution

The given transformation shows the conversion of a ketone (acetophenone) into a cyclic ketal. The formation of a cyclic ketal from a ketone requires a diol in the presence of an acid catalyst. The product shown is a 1,3-dioxolane derivative, which is a 5-membered ring containing two oxygen atoms separated by one carbon atom (the original carbonyl carbon). This specific 5-membered cyclic ketal is formed by the reaction of the ketone with a 1,2-diol. Among the given options, ethylene glycol ( HOCH ₂CH₂ OH ) is a 1,2-