What is the missing reagent in the reaction below?

Question

Quizplus · Accepted Answer

The reaction appears to be a substitution reaction where an alkyl group is being substituted with a halogen atom. The starting material is 2-butanol, which has an -OH group. For a substitution reaction to occur, the -OH group needs to be converted to a good leaving group. This is achieved using a reagent such as phosphorus tribromide (PBr3) or thionyl chloride (SOCl2). In the given reaction, only III (PBr3) is a reagent that can convert the -OH group to a good leaving group (Br) and facilitate substitution. Therefore, the best choice is C.

What Is the Missing Reagent in the Reaction Below