Answer: Option (d) is the correct answer.
Explanation:
It is known that reactivity of atoms increases on moving down the group. This is because on moving down the group there is also increase in number of shells.
As a result, outer shell electrons move away from the nucleus and thus force of attraction between the nucleus and electrons decreases.
Hence, it is easy to remove the electrons from outermost shell and thus reactivity of atom increases.
Therefore, we can conclude that the given elements are group 1 elements and largest of them is rubidium. Thus, out of the given options, rubidium element is the most reactive.
