Question

Which of the statements is/are true about the reactivity order of halogens $F_2>C{l}_2>B{r}_2>I_2.$
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 $\left(\Delta H_r\right)$ of halogenation of alkane, more reactive is the halogen.
IV. Lower the activation energy for the second chain-propagation step, more reactive is the halogen.

• A. (I), (II)
• B. (I), (II), (III)
• C. (II), (III)
• D. (II), (III), (IV)

Answer 1

Answer: (C)

(II), (III)

There are two factors 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 $\left(\Delta H_r\right)$ more reactive is the halogen.

Option C is correct.