Question

Which step is chain propagation step in the following mechanism? $(i)$ {Cl2 ->[hv] Cl^{?? + Cl^{??} $(ii)$ {Cl^{?? + CH4 -> ^{??CH3 + HCl} $(iii)$ {Cl^{?? + Cl^{?? -> Cl2} $(iv)$ {^{??CH3 + l^{??C -> CH3Cl}

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

Answer 1

Answer: (B)

$(ii)$

Answer 2

Elementary steps in which the number of free radicals consumed is equal to the number of free radicals generated are called chain propagation steps. (i): Free radicals consumed - o; Free radicals generated -2 (ii): Free radicals consumed - 1; Free radicals generated - 1 (iii): Free radicals consumed - 2; Free radicals generated - o (iv): Free radicals consumed - 2; Free radicals generated - o Thus, (ii) is a chain propagation step.