what type of reaction can be used to place the halogens in order of reactivity?

The type of reaction used to place the halogens in order of reactivity is a displacement reaction, specifically known as a halogen displacement reaction. In this reaction, a more reactive halogen can displace a less reactive halogen from its aqueous halide solution. This provides a practical way to determine their relative reactivities. The reactivity of halogens decreases down the group from Fluorine (most reactive) to Astatine (least reactive), due to factors like atomic size and electron affinity. In displacement reactions, a halogen higher in reactivity will replace a halogen lower in reactivity from its compound, illustrating the order of reactivity among halogens.