Electrophilic addition of Br₂ to the alkene double bond in butene

Steps:

• Butene (C₄H₈) is an alkene with a C=C bond that undergoes electrophilic addition with Br₂.
• Br₂ adds across the double bond following Markovnikov's rule, forming a vicinal dibromide.
• For 1-butene, addition yields 1,2-dibromobutane; for 2-butene, it yields 2,3-dibromobutane.
• The product is a saturated dibromobutane (C₄H₈Br₂) with Br atoms on adjacent carbons.

Why B is correct:

• B represents 1,2-dibromobutane, the direct product of anti addition to 1-butene's double bond per the mechanism of electrophilic addition.

Why the others are wrong:

• A is 1-bromobutane, a substitution product, not addition.
• C is 1,4-dibromobutane, requiring addition across non-adjacent carbons, impossible in this reaction.
• D is 2,2-dibromobutane, violating Markovnikov addition to form a geminal dihalide.

Final answer: B