Which one is more reactive out of fluorine and chlorine. why?

fluorine

Explanation:

because it is at the top of the halogen group, which is the second to right group on the periodic table. With halogens, the higher an element is in the column, the more reactive it is. Halogens are reactive because the outer shells that orbit the nucleus lack electrons.

also because it has low dissociation energy and the valence bonding is seen close to the nucleus hence the attraction for a new electron is greater and can gain an extra electron more easily.-if ur in a higer grade u will understand this

i'm pretty sure its b i might be wrong though!