Question

what determines periodicity in the modern periodic table? the number of neutrons; the atomic weight; the electron configuration; the number of protons in the nucleus

Explanation:

Periodicity in the modern periodic table refers to the repeating pattern of element properties. This repetition occurs because elements with similar outer electron configurations (which dictate chemical behavior) appear at regular intervals as atomic number increases. Neutron count affects isotopes, not periodicity; atomic weight was used in older periodic tables, not the modern one; proton count defines atomic number, which organizes the table but the repeating properties stem from electron configuration.

Answer:

C. The electron configuration