Electrophilic Addition Mechanism for Alkene Halogenation

Steps:

• The π electrons of 2-methylpropene attack Cl₂, forming a chloronium ion intermediate and releasing Cl⁻.
• The chloronium ion bridges the double bond, with positive charge more on the tertiary carbon due to stability.
• Cl⁻ attacks the more substituted tertiary carbon from the opposite side, leading to anti addition.
• The product is 2-chloro-2-methyl-1-chloropropane, following Markovnikov's rule for unsymmetrical alkenes.

Why B is correct:

• B accurately describes the chloronium ion as a three-membered ring intermediate, per the standard mechanism for halogen addition to alkenes.

Why the others are wrong:

• A incorrectly suggests a free radical pathway, which requires light or initiators not mentioned.
• C wrongly implies a carbocation intermediate without bridging, leading to syn addition possibilities.
• D misstates the regioselectivity, as Cl⁻ attacks the tertiary carbon, not the primary.

Final answer: B