Answer:
The Group Number of the elements.
Step-by-step explanation:
If Marie knew the group number of the elements, then she could determine the amount of valence electrons each element has and their reactivity rate. For example, if one box tells her that an element is located in group 18, then she could determine that the element is not very reactive. This is because elements in group 18 have 8 valence electrons, which makes them stable/unreactive.
Hope this helps!