Which among the following is the most reactive?

The reactivity of halogens and their compounds is primarily governed by Bond Dissociation Enthalpy. In general, interhalogen compounds ($$XY$$) are more reactive than the corresponding elemental halogens ($$X_2$$), with the notable exception of fluorine ($$F_2$$).

Since $$ICl$$ is an interhalogen compound with a weaker, polar bond compared to the elemental halogens provided, it is the most reactive.