Choose the halogen which is most reactive toward `S_(N)1` reaction in the given compound (A,B,C&D)

Options

A. `A-Br_((a)), B-I_((a)), C-Br_((a)), D-Br_((a))`
B. `A-Br_((a)), B-I_((a)), C-Br_((b)), D-Br_((a))`
C. `A-Br_((b)), B-I_((a)), C-Br_((a)), D-Br_((a))`
D. `A-Br_((b)), B-I_((b)), C-Br_((b)), D-Br_((b))`

Answer

C