Which is most reactive C-i or C-F?

C-F is more reactive than C-I. This is because the carbon-fluorine bond is stronger and more stable than the carbon-iodine bond. Fluorine is a highly electronegative element, which means it can attract electrons more strongly and form a more stable bond with carbon. This makes C-F bonds less reactive and more difficult to break compared to C-I bonds.

C-i