Which step is chain propagation step in the following mechanism?
(i) `Cl_(2) overset(hv)to Cl^(**)+Cl^(**)`
(ii) `Cl^(**)+CH_(4) to .^(**)CH_(3)+HCl`
(iii) `Cl^(**)+Cl^(**) to Cl_(2)`
(iv) `.^(**)CH_(3)+^(**)Cl to CH_(3)Cl`
A. (i)
B. (ii)
C. (iii)
D. (iv)
