Carbocation stability increases with substitution: tertiary > secondary > primary

Steps:

• Determine the carbocation formed by loss of Cl⁻ from each isomer.
• Classify each as primary, secondary, or tertiary based on the carbon attached to Cl.
• Recall that stability follows the order tertiary (most stable) > secondary > primary due to hyperconjugation and inductive effects.
• Select the isomer yielding the tertiary carbocation.

Why D is correct:

• 2-Chloro-2-methylpropane forms (CH₃)₃C⁺, a tertiary carbocation stabilized by three alkyl groups through hyperconjugation and +I effect.

Why the others are wrong:

• A: Forms primary carbocation CH₃CH₂CH₂CH₂⁺, least stable with minimal alkyl substitution.
• B: Forms secondary carbocation CH₃CH₂CH⁺CH₃, less stable than tertiary with only two alkyl groups.
• C: Forms primary carbocation (CH₃)₂CHCH₂⁺, least stable with minimal alkyl substitution.

Final answer: D