Question

Which step is chain propagation step in the following mechanism?
$\left(\right.i\left.\right)$ $Cl_{2}\overset{h v}{ \rightarrow }Cl^{\cdot }+Cl^{\cdot }$
$\left(\right.ii\left.\right)$ $Cl^{\cdot }+CH_{4} \rightarrow ^{\cdot }CH_{3}+HCl$
$\left(\right.iii\left.\right)$ $Cl^{\cdot }+Cl^{\cdot } \rightarrow Cl_{2}$
$\left(\right.iv\left.\right)$ $^{\cdot }CH_{3}+^{\cdot }Cl \rightarrow CH_{3}Cl$

• A. (i)
• B. (ii)
• C. (iii)
• D. (iv)

Answer 1

Answer: (B)

Photo chlorination of methane occurs in three steps i.e. initiation, propagation and termination.
Chain propagating step is $\text{Cl}^{\cdot } + \text{CH}_{4} \rightarrow \_{}^{\text{.}}\text{C} \text{H}_{3} + \text{HCl}$ .