In a halogen displacement reaction, one halogen displaces another in a compound. Whether or not the reaction occurs depends on the reactivity of the halogens. The order of reactivity is the same as the order of the elements from top to bottom in the halogen group (group 7/VIIA), so fluorine is the most reactive and iodine is the least reactive halogen.Example: Will the following single displacement (single replacement) reaction occur?#Cl2 + 2NaBr --> Br2 + 2NaClYes. The reaction will occur because Cl is above Br on the Periodic Table, so it is more reactive than Br so it will displace (replace) Br in the compound NaBr.Example:Will the reverse reaction take place?Br2 + 2NaCl --> Cl2 + 2NaBrNo. Br is below Cl on the periodic table, so it cannot displace (replace) Cl from the NaCl compound.