Question

The most reactive elements in the halogen group is ________________.
A.Astatine
B.Iodine
C.Chlorine
D.Fluorine

Answer 1

The reactivity of an element in the periodic table is dependent upon its ability to give up or take up electrons. The higher is the ability to accept or give up electrons, the higher will be the reactivity.

Complete Step by step Solution:
Fluorine is the smallest element is the halogen family while astatine is the largest one. So with seven electrons in the valence shell, it is only one electron short of the octet configuration. So it readily accepts an electron to complete the octet. On the other hand, as we move down the group, the effect of the nuclear charge on the valence shell electrons loosens up due to the increasing distance between the nucleus and the valence shell. Hence when any electron is added to the valence shell to fill up the octet configuration, there is not much attraction between the nucleus and the valence shell electrons due to which the atom does not become stable. Hence the reactivity decreases as we move down the group, in case of the halogens.

So, the correct answer is option D.

Notes: The case of reactivity is just the opposite of the halogens, in case of the alkali metals. This is because of the same reason as explained here. As alkali metals give up electrons to attain octet configuration, so the reactivity depends on the ease of release of the valence shell electron, which increases as we move down the group when the distance between the nucleus increases and the electrons are more easily released.