Atomic Mass.
Reactivity decreases as you go down a group.
Atomic Radius also decreases as you go down a group.
Valence electrons are the same within a group.
Atomic mass, however, increases as you go down a group.
Hope this helps!
Explanation:
When we move down a group then there will be increase in number of shells present in an atom. Due to this there will be increase in atomic radii of the atom.
As a result, there will be increase in atomic mass of the atom also. Whereas reactivity of metals increases on moving down the group as the valence shell moves away from the nucleus. So, it becomes easy for the metal atom to lose an electron.
On the other hand, reactivity of non-metals decreases on moving down the group.
So, we can conclude that properties increase when moving down a group of the periodic table are atomic radii and atomic mass.
