Chlorine, bromine and iodine are Group 7 elements. A student investigated the reactivity of these elements.
The student added:
- aqueous chlorine to potassium bromine and potassium iodide solutions
- aqueous bromine to potassium chloride and potassium iodide solutions
- aqueous iodine to potassium chloride and potassium bromide solutions.
The student's results are shown below.

Solution | Potassium chloride | Potassium bromide | Potassium iodide

Chlorine | None | Solution turned orange-brown | Solution turned brown
Bromine | No reaction | None | Solution turned brown
Iodine | No reaction | No reaction | None

Use these results to state and explain the trend in reactivity of these Group 7 elements. (2)