Explanation

(b)
The addition of propene to $HBr$ opposes the Markownikoff’s rule in presence of organic peroxide.
$CH_{3}CH = CH_{2} + HBr\underset{peroxide}{\overset{Organic}{\rightarrow}}CH_{3}CH_{2}CH_{2}Br$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ n$-propyl bromide
It is also called the Kharash effect or $anti$-Markownikoff’s rule.