What happens to the size of halogen atoms as you go down the group?

As you move down the group of halogens in the periodic table, the size of the halogen atoms increases. This increase in atomic size is primarily due to the addition of electron shells as you progress down the group. Each successive element has one more shell of electrons than the element above it, which means that the outermost electrons are situated further from the nucleus.

Additionally, although the nuclear charge (the number of protons) increases as you go down the group, this is partially offset by the effects of electron shielding. The inner electron shells shield the outer electrons from the attractive force of the nucleus, allowing the outer electrons to be located at a greater distance from the center of the atom.

Consequently, as you go down the group, the overall effect is that the size of the atom increases, making the correct answer A.