Question

the chemical elements display periodicity when theyre arranged according to
a) atomic number.
b) atomic volume.
c) atomic weight.
d) atomic mass.

Explanation:

The periodic table of elements is arranged by atomic number (the number of protons in an atom's nucleus). When elements are ordered by atomic number, their chemical and physical properties repeat periodically. Atomic volume, atomic weight (which is related to atomic mass, the mass of an atom), do not serve as the basis for the periodic arrangement; the modern periodic law is based on atomic number.

Answer:

A) atomic number.