The reaction between ethene C2H4 and hydrogen bromide HBr is an example of an electrophilic addition reaction. The mechanism for this reaction involves two main steps, and the intermediate formed is a carbocation. Here's the detailed mechanism:1. Electrophilic attack on the alkene:Ethene has a double bond between the two carbon atoms, which consists of a sigma bond and a pi bond. The bond has a high electron density, making it nucleophilic. On the other hand, hydrogen bromide is a polar molecule, with the hydrogen atom being partially positive + and the bromine atom being partially negative - . This makes the hydrogen atom in HBr an electrophile.The nucleophilic electrons of the double bond in ethene attack the electrophilic hydrogen atom in HBr, forming a new C-H bond. Simultaneously, the H-Br bond breaks, and the electrons from the bond move to the bromine atom, forming a negatively charged bromide ion Br- .2. Formation and reaction of the carbocation intermediate:When the bond in ethene attacks the hydrogen atom, one of the carbon atoms loses its share of the electrons, resulting in a positively charged carbocation intermediate. In this case, since both carbon atoms in ethene are equivalent, the carbocation can be formed on either carbon atom.The carbocation is a highly reactive intermediate due to its positive charge. The negatively charged bromide ion Br- acts as a nucleophile and attacks the positively charged carbon atom in the carbocation, forming a new C-Br bond.The final product of this reaction is bromoethane C2H5Br , formed by the addition of HBr across the double bond in ethene. The nature of the intermediate involved in this reaction is a carbocation, which is stabilized by the neighboring carbon atom through hyperconjugation.