Question

Why would Cl₂ react with Br but not I₂?

Answer 1

Chlorine is more reactive than bromine and can replace it in a halogen replacement reaction.

Step-by-step explanation:

The reactivity of the halogen group (group 17) decreases from top to bottom within the group. Fluorine is the most reactive halogen, while iodine is the least. Since chlorine is above bromine, it is more reactive than bromine and can replace it in a halogen replacement reaction.

Answer 2

That means that chlorine is a more powerful oxidising agent than either bromine or iodine as the reduction potential of Cl2 is higher than that of Br2 and I2.