Final answer:
Atoms of the same element may have different masses.
Step-by-step explanation:
The correct statement according to modern atomic theory is that atoms of the same element may have different masses. This is because atoms of the same element can have different numbers of neutrons, resulting in different isotopes with varying masses. For example, carbon-12 and carbon-14 are both isotopes of carbon, but they have different masses due to the difference in the number of neutrons.
Learn more about modern atomic theory