Atoms of elements at the top of a group on the periodic table are smaller than the atoms of elements at the bottom of the group. how does this explain the difference in the reactivity of meals within a group

The metals near the bottom are more reactive for alkali metals as the electrons lost to react are furthest away from the atomic nucleus so have a much lower force of attraction. This means they can react with less activation energy so react faster and are more reactive

The answer is d) by requesting advice on science internet sites