The Grignard reaction is a very important organometallic chemical reaction where the Grignard reagent ( alkyl, vinyl, or aryl-magnesium halides) acts as nucleophile in order to the formation of Carbon-Carbon bonds.
In the problem, the phenylmagnesium chloride is the grignard reagent. The volume of 2.0 M phenylmagnesium chloride solution you need to add 2.9 mmol is:
To balance the the chemical reaction, the number of moles
per element is balance is both side of the reaction and also the charge in both
sides of the reation. to balnce the reaction: