Assertion: The fluorine has lower reactivity.
Reason: F – F bond has lower bond dissociation energy.
A. Both assertion and reason are true and the reason is a correct explanation of the assertion.
B. Both assertion and reason are true but reason is not a correct explanation of the assertion.
C. Assertion is true but reason is false
D. Both the assertion and reason are false.
E. Assertion is false but the reason is true.

Hint: Fluorine is a lightest halogen and exists as a highly toxic pale yellow diatomic gas at standard conditions. Fluorine is important in creating nuclear material for nuclear power plants and insulating electrical towers.

Complete step by step answer:
Let us first know a bit about fluorine.
Fluorine is the first element in the halogen group in the periodic table and it’s a gas at room temperature. As we know that it is the top element in the Halogen group, and therefore, it is very reactive.
Now, let us see about the reactivity of fluorine.
As we know fluorine is the most electronegative element on the periodic table, which implies that it is a very strong oxidizing agent. There is a periodic trend for electronegativity, basically it starts at bottom left with francium having the lowest electronegativity and goes diagonally left to right all the way up to fluorine having the highest electronegativity.
Now, let us see about the bond dissociation energy of fluorine.
Fluorine has a very small radius due to the positive protons which have a very strong attraction to the negative electrons, holding them closer to the nucleus than the bigger and less electronegative elements. Due to which the F – F bond length is short. Therefore, electrons lie very close to each other and very large electron-electron (Interelectronic) repulsions take place which weakens the bond.
Hence, the assertion is false but the reason is true. Therefore, option E is the required answer.

Note: Fluorine gas is very irritating and very dangerous to the eyes, skin and lungs. At higher concentration, it becomes hard to breath. Exposure to high concentrations can cause death to lung damage.