Fluorine is the most reactive of all four common halogens.

Explanation

**Step-by-Step Solution:**

1. **Understanding Halogens:**
- The halogens are a group of elements in Group 17 of the periodic table, which include fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). These elements are known for their high reactivity.

2. **Reactivity Trend:**
- Among the halogens, reactivity decreases as you move down the group from fluorine to iodine. This is due to the increasing atomic size and the corresponding increase in the distance of the outer electrons from the nucleus.

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