Addition of $\mathrm{HBr}$ to propene gives 2 - bromo propane, this reaction is intiated by

 Formation of 2-Bromopropane: Addition to $\mathrm{HBr}$ to propene is an ionic electrophilic addition reaction in which the electrophile, $\left({\mathrm{H}}^{+}\right)$adds to form a more stable $2°$ carbocation. In the 2 nd reaction, the carbocation is rapidly attacked by the nucleophile $\left({\mathrm{Br}}^{-}\right)$to form 2-bromopropane.

$\mathrm{H}-\mathrm{Br}\rightleftharpoons {\mathrm{H}}^{+}+{\mathrm{Br}}^{-}$

(i) ${\mathrm{CH}}_3\to -\mathrm{CH}={\mathrm{CH}}_2+{\mathrm{H}}^{+}\stackrel{\mathrm{Slow}}{⟶}$$+\mathrm{l}$ effect

Electrophile

 $\underset{2°\mathrm{Carbocation}}{{\mathrm{CH}}_3-\mathrm{CH}}-{\mathrm{CH}}_3$

Hence the correct option is (A).