Which of the statement is/are true about the reactivity of halogenation of alkanes ? The reactivity ordar is `F_(2) gt C1_(2) gt Br_(2) gt I_(2)` .
I. Lower the activation energy for the chain initiation step, more reactive is the halogen.
II. Lower the activation energy for the first chain propagation step, more reactive is the halogen.
III. More negative is the overall heat of the reaction `(Delta H_(r)^(@))` of halogenation ofg alkane, more reactive is the halogen.
IV. Lower the activation energy for the second chain-propagation step, more reactives is the halogen.

Options

A. (a) (I), (II)
B. (b) (I), (II), (III)
C. (c) (II),(III)
D. (d) (II), (III), (IV)

Answer

C

Explanation

There are two factor that determine the reactivity of the halogenation of alkanes.
1. Lesser the positive value of `E_(act)` of the first chain propagating step, more reactive is the halogen.
2. Higher the negative value of overall heat of reaction `(Delta H_(r)^(@))` , more reactive is the halogen. This explains high reactivity and explosive violence with which `F_(2)` reacts with `CH_(4)` .