An organic compound [A] reacts with and forms compound [B] which reacts with magnesium in presence…

An organic compound [A] reacts with $\text{PBr}_3$ and forms compound [B] which reacts with magnesium in presence of ether and gives a Grignard’s reagent. This Grignard’s reagent reacts with $\text{CH}_3\text{CHO}$ followed by hydrolysis to form secondary propyl alcohol. Identify the compounds [A] and [B]. Write the chemical reaction to show how acetaldehyde is converted to secondary propyl alcohol.