The elements in Group 7 are called the halogens.
A more reactive halogen can displace a less reactive halogen from a solution of its salt.
Which combination of solutions will produce a reaction when mixed?

In Group 7 (the halogens), reactivity decreases as you go down the group. The order of reactivity is Fluorine > Chlorine > Bromine > Iodine. A displacement reaction occurs when a more reactive halogen displaces a less reactive halide ion from its salt solution. - **A: Chlorine and potassium fluoride:** Chlorine is below fluorine, so it is less reactive and cannot displace fluoride. No reaction. - **B: Chlorine and potassium bromide:** Chlorine is above bromine, so it is more reactive and can displace bromide. Reaction occurs: Cl₂(aq) + 2KBr(aq) → 2KCl(aq) + Br₂(aq). - **C: Bromine and potassium fluoride:** Bromine is below fluorine, so it is less reactive and cannot displace fluoride. No reaction. - **D: Bromine and potassium chloride:** Bromine is below chlorine, so it is less reactive and cannot displace chloride. No reaction.