This reaction is an acid-catalyzed substitution reaction, where ethanol CH3CH2OH reacts with hydrobromic acid HBr to form bromoethane CH3CH2Br and water H2O . The major intermediate in this reaction is the formation of a carbocation. Here is the proposed mechanism:Step 1: Protonation of the alcoholThe lone pair of electrons on the oxygen atom of ethanol attacks the hydrogen atom of HBr, forming a bond with it. This results in the formation of an oxonium ion protonated ethanol and a bromide ion Br- .CH3CH2OH + HBr CH3CH2OH2+ + Br-Step 2: Formation of carbocationThe oxonium ion CH3CH2OH2+ is unstable and undergoes heterolysis, where the bond between the oxygen and the carbon atom breaks. The electrons in the bond move to the oxygen atom, resulting in the formation of a carbocation CH3CH2+ and a water molecule H2O .CH3CH2OH2+ CH3CH2+ + H2OStep 3: Nucleophilic attackThe bromide ion Br- acts as a nucleophile and attacks the carbocation CH3CH2+ , forming a bond with the carbon atom. This results in the formation of bromoethane CH3CH2Br .CH3CH2+ + Br- CH3CH2BrOverall, the major intermediate in this reaction is the carbocation CH3CH2+ , and the mechanism involves protonation of the alcohol, formation of a carbocation, and nucleophilic attack by the bromide ion.