Predict the major product formed when $HCl$ is added to $2-$methylprop$-1-$ene $(isobutylene)$. Explain the mechanism involved.

(N/A) The addition of $HCl$ to $2-$methylprop$-1-$ene follows Markovnikov's rule,where the nucleophile $(Cl^-)$ attaches to the more substituted carbon atom.
Reaction:
$CH_3-C(CH_3)=CH_2 + HCl \rightarrow CH_3-C(Cl)(CH_3)-CH_3$ ($2-$chloro$-2-$methylpropane).
Mechanism:
Step-$1$: Formation of carbocation.
The electrophile $H^+$ attacks the double bond to form a carbocation. The $3^\circ$ carbocation $(CH_3-C^+(CH_3)-CH_3)$ is more stable than the $1^\circ$ carbocation $(CH_3-CH(CH_3)-CH_2^+)$,so the $3^\circ$ carbocation is formed preferentially.
Step-$2$: Attack of nucleophile.
The nucleophile $Cl^-$ attacks the $3^\circ$ carbocation to form the final product,$2-$chloro$-2-$methylpropane.