Question

Which halogen cannot replace any other halogen from their compounds?

Answer 1

Iodine is the answer to your question

The replacing depends on the reactivity of a compound.
You will study the reactivity order of halogens very detail in Class 12 Chemistry.

Reactivity of Halogen decreases down the group. ie F > Cl > Br>I
So, F can replace Cl , Br , I
Cl can replace Br , I
Br can replace I
Iodine cannot replace any other halogen from their compounds.

So, the answer here is Iodine.

Note : A similar question may be asked which halogen is never replaced by any of the other halogens from their compounds.
There the answer will be Flourine