The correct answer is A. Fluorine.
Fluorine is the most reactive halogen because it has the smallest atomic radius and the highest electronegativity. This means that it has the strongest attraction for electrons, and is therefore more likely to form bonds with other elements.
Chlorine is the second most reactive halogen, followed by bromine and iodine. These elements become less reactive as their atomic radii increase and their electronegativities decrease.
Here
is a table of the halogens, with their atomic radii and electronegativities:Element | Atomic radius (pm) | Electronegativity
——- | ——– | ——–
Fluorine | 71 | 4.0
Chlorine | 99 | 3.0
Bromine | 114 | 2.8
Iodine | 133 | 2.5
As you can see, fluorine has the smallest atomic radius and the highest electronegativity. This means that it has the strongest attraction for electrons, and is therefore more likely to form bonds with other elements.