# Displacement reactions of Halide ions

I understand that the reactivity decreases as you go down group 7. In displacement reactions the more reactive halide replaces the least reactive halide, but in this question i do not understand the use of hexane in determining their reactivity series. I also do not understand why 5 test tubes give a purple layer as iodine should not react with sodium bromide.

• For future reference, please crop your screen shot to just the question of interest or use LaTeX tables. – Zhe Jun 2 '17 at 17:37
• Halogens belong to group 17 not 7 – chail10 Jun 2 '17 at 19:55

I think you've already correctly identified that $\ce{Br2}$ and $\ce{Cl2}$ will react with $\ce{NaI(aq)}$ to produce $\ce{I2}$. The part you didn't consider is that $\ce{I2}$ is present in every mixture in the bottom row of that table because no displacement will occur. Therefore, the hexane solution will be purple.