Question

Which of the following statement regarding free radical halogenation of alkane is not true?
(A) Hadrogen abstraction by halogen radical in the propagation step is exothermic in both chlorination and bromination
(B) Hydrogen abstraction by halogen radical in the propagation step is exothermic in cholorination but endothermic in bromination

Answer 1

Since, abstraction of $H$ by chlorine is fast process it result in exothermic propagation step resulting in less stable radical intermediate where as, there is slow process by bromine resulting in full development of radical character (stable) which require energy or endothermic.