Question

which have different numbers of electrons?
different ions of an element
different isotopes of an element
the nucleus of an element
each of the atoms of an element

Explanation:

Ions are formed by the gain or loss of electrons. Different ions of an element have different numbers of electrons. Isotopes have the same number of electrons as they are the same element with different neutrons. The nucleus contains protons and neutrons, not electrons. Atoms of an element in their neutral state have the same number of electrons equal to the number of protons.

Answer:

A. different ions of an element