Final answer:
The theory that interactions between atoms depend mostly on the arrangement of the outermost electrons is best supported by similar reactions among elements in a group (column) of the periodic table.
Step-by-step explanation:
The periodic table is a tabular arrangement of chemical elements organized by their atomic number, electron configuration, and recurring chemical properties. Elements are grouped into periods (rows) and groups (columns). This systematic representation allows for the prediction of an element's properties based on its position in the table.
The theory that interactions between atoms depend mostly on the arrangement of the outermost electrons is best supported by the observation of similar reactions among elements in a group (column) of the periodic table. Elements within the same group have the same number of electrons in their outermost energy level, also known as the valence shell. This similarity in electron arrangement is what leads to similar chemical reactivity among elements in the same group.