Final answer:
The reactivity of halogens is related to the shielding effect because of the presence of inner-shell electrons shielding the valence electrons from the attractive pull of the nucleus.
Step-by-step explanation:
The reactivity of the halogens is related to the shielding effect. The shielding effect refers to the blocking of valence shell electron attraction by the nucleus, due to the presence of inner-shell electrons.
In the case of halogens, they have 7 valence electrons, which means their valence shell is only one electron away from being full. This makes halogens highly reactive as they tend to gain one electron in order to achieve a stable octet configuration.