Final answer:
The atomic number is the key factor in determining the force of attraction between the outermost electrons and the nucleus for elements in the same column of the periodic table.
Step-by-step explanation:
When comparing elements in the same column of the periodic table, the atomic number is the dominant factor for determining the attractive force between the outermost electrons and the nucleus. As we move down a group in the periodic table, the atomic number increases, which means that more protons are in the nucleus, creating a stronger positive charge to attract electrons. However, the addition of more electron shells increases atomic size, which can counteract the increased nuclear charge to some extent. Considering this, atomic number is still the most significant factor because it directly relates to the number of protons in the nucleus, which establishes the effective nuclear charge exerted on the valence electrons.