The electrophilic addition reaction of hydrogen halides HBr, HCl, HI with alkenes involves the following steps:Step 1: Protonation of the alkeneThe reaction begins with the alkene acting as a nucleophile electron-rich species and the hydrogen halide acting as an electrophile electron-poor species . The alkene's double bond donates a pair of electrons to the hydrogen atom of the hydrogen halide, forming a new C-H bond. This results in the formation of a carbocation intermediate and a halide ion Br-, Cl-, or I- .Step 2: Formation of the carbocation intermediateThe carbocation intermediate is formed when one of the carbon atoms in the alkene gains a positive charge. This occurs because the carbon atom loses its share of the electron pair that formed the double bond. The stability of the carbocation intermediate depends on the number of alkyl groups attached to the positively charged carbon atom. More alkyl groups lead to a more stable carbocation due to the inductive effect and hyperconjugation.Step 3: Nucleophilic attack by the halide ionThe halide ion Br-, Cl-, or I- acts as a nucleophile and attacks the positively charged carbon atom in the carbocation intermediate. This results in the formation of a new C-X bond where X is the halide , yielding the final alkyl halide product.Overall, the electrophilic addition reaction of hydrogen halides with alkenes follows a two-step mechanism:1. Protonation of the alkene to form a carbocation intermediate.2. Nucleophilic attack by the halide ion to form the alkyl halide product.This mechanism is supported by experimental evidence, such as the observation of carbocation rearrangements in some reactions, which indicates the presence of a carbocation intermediate. Additionally, the regioselectivity of the reaction can be explained by Markovnikov's rule, which states that the hydrogen atom will preferentially bond to the carbon atom with the most hydrogen atoms already attached, leading to the more stable carbocation intermediate.