Question

1. according to modern atomic theory, what is the primary difference between isotopes of the same element?

they have a different number of electrons.
they have a different atomic number.
they have a different number of neutrons.
they have a different number of protons.
clear all

Explanation:

Isotopes of the same element have the same atomic number (number of protons) because the atomic number defines the element. Electrons can vary in ions but not for isotopes' primary difference. Isotopes differ in the number of neutrons, which affects the mass number. So the correct option is the one stating they have a different number of neutrons.

Answer:

The option: "They have a different number of neutrons." (the third option in the list)