Electrophilic addition mechanism for HBr to ethene

Steps:

• π bond of ethene attacks Hδ+ from HBr, heterolytically cleaving H-Br bond.
• Forms ethyl carbocation intermediate +CH2-CH3 (or H2C-CH3 with + on first C) and free Brδ-.
• Brδ- nucleophilically attacks positively charged carbon.
• Yields CH3-CH2Br as product, following Markovnikov orientation (symmetric here).

Why B is correct:

• Depicts carbocation intermediate H2C-CH2+ with separate Brδ-, matching H+ addition first per electrophilic addition rule.

Why the others are wrong:

• A: Intermediate H3C-CHBr+ implies Br+ electrophile, violating HBr polarity.
• C: Labels Brδ+, contradicting HBr's partial charges (Hδ+, Brδ-).
• D: Intermediate H2C-CHBr+ wrongly attaches Brδ- early, suggesting nucleophilic addition.

Final answer: B