Question

Fluorine is the most reactive among all the halogens, because of its

• A. small size
• B. low dissociation energy of $F-F$ bond
• C. large size
• D. high dissociation energy of $F-F$ bond.

Answer 1

Answer: (B)

Fluorine is the most reactive among all the halogens, because of it's low dissociation energy of $F-F$ bond. The dissociation energies $(kcal/mol)$ in $F_2,C{l}_2,B{r}_2$ and $I_2$ are $38,57,45.5$ and $35.6$ respectively.
In the case of fluorine:
(a) short bond length and larger repulsion between non-bonding electrons lead to low dissociation energy.
(b) absence of multiple bonding leads to low dissociation energy.