In Group 7 (halogens), how does reactivity change as you move down the group?

• A. Increases down the group
• B. Increases then decreases
• C. No trend
• D. Decreases down the group

Answer: (D)

The main idea is how easily a halogen can attract and gain an electron to form a halide ion. In Group 7, moving down the group means the atoms get larger and more shielded by inner electrons, so the outer electrons feel a weaker pull from the nucleus. This makes it harder for the atom to attract an extra electron, so its reactivity as an oxidizing agent decreases. Electron affinity also becomes less exothermic down the group, reinforcing the trend. That’s why fluorine is the most reactive and reactivity falls as you go to chlorine, bromine, and iodine.